Advantage of switch over if-else statement

Question

What s the best practice for using a switch statement vs using an if statement for 30 unsigned enumerations where about 10 have an expected action  that presently is the same action   Performance and space need to be considered but are not critical   I ve abstracted the snippet so don t hate me for the naming conventions   switch statement      numError is an error enumeration type  with 0 being the non-error case    fire special event   is a stub method for the shared processing  switch  numError        case ERROR 01       intentional fall-through   case ERROR 07       intentional fall-through   case ERROR 0A       intentional fall-through   case ERROR 10       intentional fall-through   case ERROR 15       intentional fall-through   case ERROR 16       intentional fall-through   case ERROR 20            fire special event          break     default             error codes that require no additional action       break             if statement   if   ERROR 01    numError           ERROR 07    numError           ERROR 0A    numError            ERROR 10    numError           ERROR 15    numError           ERROR 16    numError           ERROR 20    numError       fire special event

User · Answer

Im not the person to tell you about speed and memory usage  but looking at a switch statment is a hell of a lot easier to understand then a large if statement  especially 2-3 months down the line

User · Answer

Use switch   In the worst case the compiler will generate the same code as a if-else chain  so you don t lose anything  If in doubt put the most common cases first into the switch statement   In the best case the optimizer may find a better way to generate the code  Common things a compiler does is to build a binary decision tree  saves compares and jumps in the average case  or simply build a jump-table  works without compares at all

User · Answer

Aesthetically I tend to favor this approach   unsigned int special events           ERROR 01      ERROR 07      ERROR 0A      ERROR 10      ERROR 15      ERROR 16      ERROR 20      int special events length   sizeof  special events    sizeof  unsigned int     void process event unsigned int numError         for  int i   0  i  lt  special events length  i               if  numError    special events i                  fire special event                 break                           Make the data a little smarter so we can make the logic a little dumber   I realize it looks weird   Here s the inspiration  from how I d do it in Python    special events         ERROR 01      ERROR 07      ERROR 0A      ERROR 10      ERROR 15      ERROR 16      ERROR 20        def process event numError       if numError in special events           fire special event

User · Answer

I know its old but  public class SwitchTest   static final int max   100000   public static void main String   args     int counter1   0  long start1   0l  long total1   0l   int counter2   0  long start2   0l  long total2   0l  boolean loop   true   start1   System currentTimeMillis    while  true      if  counter1    max        break      else       counter1          total1   System currentTimeMillis   - start1   start2   System currentTimeMillis    while  loop      switch  counter2        case max        loop   false        break      default        counter2          total2   System currentTimeMillis   - start2   System out println  While if else      total1    ms    System out println  Switch      total2    ms    System out println  Max Loops      max    System exit 0         Varying the loop count changes a lot    While if else  5ms Switch  1ms Max Loops  100000  While if else  5ms Switch  3ms Max Loops  1000000  While if else  5ms Switch  14ms Max Loops  10000000  While if else  5ms Switch  149ms Max Loops  100000000   add more statements if you want

User · Answer

Use switch   In the worst case the compiler will generate the same code as a if-else chain  so you don t lose anything  If in doubt put the most common cases first into the switch statement   In the best case the optimizer may find a better way to generate the code  Common things a compiler does is to build a binary decision tree  saves compares and jumps in the average case  or simply build a jump-table  works without compares at all

User · Answer

When it comes to compiling the program  I don t know if there is any difference  But as for the program itself and keeping the code as simple as possible  I personally think it depends on what you want to do  if else if else statements have their advantages  which I think are   allow you to test a variable against specific ranges you can use functions  Standard Library or Personal  as conditionals    example    int a   cout lt  lt  enter value  n    cin gt  gt a    if  a  gt  0  amp  amp  a  lt  5            cout lt  lt  a is between 0  5 n        else if a  gt  5  amp  amp  a  lt  10        cout lt  lt  a is between 5 10 n        else           a is not an integer  or is not in range 0 10 n     However  If else if else statements can get complicated and messy  despite your best attempts  in a hurry  Switch statements tend to be clearer  cleaner  and easier to read  but can only be used to test against specific values  example    int a   cout lt  lt  enter value  n    cin gt  gt a    switch a         case 0      case 1      case 2       case 3      case 4      case 5          cout lt  lt  a is between 0 5 and equals    lt  lt a lt  lt   n           break        other case statements     default          cout lt  lt  a is not between the range or is not a good value n          break    I prefer if - else if - else statements  but it really is up to you  If you want to use functions as the conditions  or you want to test something against a range  array  or vector and or you don t mind dealing with the complicated nesting  I would recommend using If else if else blocks  If you want to test against single values or you want a clean and easy to read block  I would recommend you use switch   case blocks

User · Answer

switch is definitely preferred   It s easier to look at a switch s list of cases  amp  know for sure what it is doing than to read the long if condition     The duplication in the if condition is hard on the eyes   Suppose one of the    was written     would you notice   Or if one instance of  numError  was written  nmuError   which just happened to compile   I d generally prefer to use polymorphism instead of the switch  but without more details of the context  it s hard to say   As for performance  your best bet is to use a profiler to measure the performance of your application in conditions that are similar to what you expect in the wild   Otherwise  you re probably optimizing in the wrong place and in the wrong way

User · Answer

Im not the person to tell you about speed and memory usage  but looking at a switch statment is a hell of a lot easier to understand then a large if statement  especially 2-3 months down the line

User · Answer

The switch is faster   Just try if else-ing 30 different values inside a loop  and compare it to the same code using switch to see how much faster the switch is   Now  the switch has one real problem    The switch must know at compile time the values inside each case  This means that the following code      WON T COMPILE extern const int MY VALUE    void doSomething const int p iValue        switch p iValue               case MY VALUE      do something      break          default      do something else      break             won t compile   Most people will then use defines  Aargh    and others will declare and define constant variables in the same compilation unit  For example      WILL COMPILE const int MY VALUE   25    void doSomething const int p iValue        switch p iValue               case MY VALUE      do something      break          default      do something else      break             So  in the end  the developper must choose between  speed   clarity  vs   code coupling     Not that a switch can t be written to be confusing as hell    Most the switch I currently see are of this  confusing  category     But this is another story         Edit 2008-09-21       bk1e added the following comment   Defining constants as enums in a header file is another way to handle this        Of course it is       The point of an extern type was to decouple the value from the source  Defining this value as a macro  as a simple const int declaration  or even as an enum has the side-effect of inlining the value  Thus  should the define  the enum value  or the const int value change  a recompilation would be needed  The extern declaration means the there is no need to recompile in case of value change  but in the other hand  makes it impossible to use switch  The conclusion being Using switch will increase coupling between the switch code and the variables used as cases  When it is Ok  then use switch  When it isn t  then  no surprise          Edit 2013-01-15       Vlad Lazarenko commented on my answer  giving a link to his in-depth study of the assembly code generated by a switch  Very enlightning  http   lazarenko me switch

User · Answer

I would say use SWITCH  This way you only have to implement differing outcomes  Your ten identical cases can use the default  Should one change all you need to is explicitly implement the change  no need to edit the default  It s also far easier to add or remove cases from a SWITCH than to edit IF and ELSEIF   switch numerror       ERROR 20     fire special event      break      default     null    break      Maybe even test your condition  in this case numerror  against a list of possibilities  an array perhaps so your SWITCH isn t even used unless there definately will be an outcome

User · Answer

I would pick the if statement for the sake of clarity and convention  although I m sure that some would disagree  After all  you are wanting to do something if some condition is true  Having a switch with one action seems a little    unneccesary

User · Answer

switch is definitely preferred   It s easier to look at a switch s list of cases  amp  know for sure what it is doing than to read the long if condition     The duplication in the if condition is hard on the eyes   Suppose one of the    was written     would you notice   Or if one instance of  numError  was written  nmuError   which just happened to compile   I d generally prefer to use polymorphism instead of the switch  but without more details of the context  it s hard to say   As for performance  your best bet is to use a profiler to measure the performance of your application in conditions that are similar to what you expect in the wild   Otherwise  you re probably optimizing in the wrong place and in the wrong way

User · Answer

Seeing as you only have 30 error codes  code up your own jump table  then you make all optimisation choices yourself  jump will always be quickest   rather than hope the compiler will do the right thing  It also makes the code very small  apart from the static declaration of the jump table   It also has the side benefit that with a debugger you can modify the behaviour at runtime should you so need  just by poking the table data directly

User · Answer

Use switch  it is what it s for and what programmers expect   I would put the redundant case labels in though - just to make people feel comfortable  I was trying to remember when   what the rules are for leaving them out  You don t want the next programmer working on it to have to do any unnecessary thinking about language details  it might be you in a few months time

User · Answer

I would say use SWITCH  This way you only have to implement differing outcomes  Your ten identical cases can use the default  Should one change all you need to is explicitly implement the change  no need to edit the default  It s also far easier to add or remove cases from a SWITCH than to edit IF and ELSEIF   switch numerror       ERROR 20     fire special event      break      default     null    break      Maybe even test your condition  in this case numerror  against a list of possibilities  an array perhaps so your SWITCH isn t even used unless there definately will be an outcome

User · Answer

Use switch  it is what it s for and what programmers expect   I would put the redundant case labels in though - just to make people feel comfortable  I was trying to remember when   what the rules are for leaving them out  You don t want the next programmer working on it to have to do any unnecessary thinking about language details  it might be you in a few months time

User · Answer

I would say use SWITCH  This way you only have to implement differing outcomes  Your ten identical cases can use the default  Should one change all you need to is explicitly implement the change  no need to edit the default  It s also far easier to add or remove cases from a SWITCH than to edit IF and ELSEIF   switch numerror       ERROR 20     fire special event      break      default     null    break      Maybe even test your condition  in this case numerror  against a list of possibilities  an array perhaps so your SWITCH isn t even used unless there definately will be an outcome

User · Answer

The switch is faster   Just try if else-ing 30 different values inside a loop  and compare it to the same code using switch to see how much faster the switch is   Now  the switch has one real problem    The switch must know at compile time the values inside each case  This means that the following code      WON T COMPILE extern const int MY VALUE    void doSomething const int p iValue        switch p iValue               case MY VALUE      do something      break          default      do something else      break             won t compile   Most people will then use defines  Aargh    and others will declare and define constant variables in the same compilation unit  For example      WILL COMPILE const int MY VALUE   25    void doSomething const int p iValue        switch p iValue               case MY VALUE      do something      break          default      do something else      break             So  in the end  the developper must choose between  speed   clarity  vs   code coupling     Not that a switch can t be written to be confusing as hell    Most the switch I currently see are of this  confusing  category     But this is another story         Edit 2008-09-21       bk1e added the following comment   Defining constants as enums in a header file is another way to handle this        Of course it is       The point of an extern type was to decouple the value from the source  Defining this value as a macro  as a simple const int declaration  or even as an enum has the side-effect of inlining the value  Thus  should the define  the enum value  or the const int value change  a recompilation would be needed  The extern declaration means the there is no need to recompile in case of value change  but in the other hand  makes it impossible to use switch  The conclusion being Using switch will increase coupling between the switch code and the variables used as cases  When it is Ok  then use switch  When it isn t  then  no surprise          Edit 2013-01-15       Vlad Lazarenko commented on my answer  giving a link to his in-depth study of the assembly code generated by a switch  Very enlightning  http   lazarenko me switch

User · Answer

while  true     while  loop    Probably the first one is optimised by the compiler  that would explain why the second loop is slower when increasing loop count

User · Answer

I agree with the compacity of the switch solution but IMO you re hijacking the switch here  The purpose of the switch is to have different handling depending on the value  If you had to explain your algo in pseudo-code  you d use an if  because  semantically  that s what it is  if whatever error do this    So unless you intend someday to change your code to have specific code for each error  I would use if

User · Answer

while  true     while  loop    Probably the first one is optimised by the compiler  that would explain why the second loop is slower when increasing loop count

User · Answer

I m not sure about best-practise  but I d use switch - and then trap intentional fall-through via  default

User · Answer

Code for readability   If you want to know what performs better  use a profiler  as optimizations and compilers vary  and performance issues are rarely where people think they are

User · Answer

I would pick the if statement for the sake of clarity and convention  although I m sure that some would disagree  After all  you are wanting to do something if some condition is true  Having a switch with one action seems a little    unneccesary

User · Answer

I know its old but  public class SwitchTest   static final int max   100000   public static void main String   args     int counter1   0  long start1   0l  long total1   0l   int counter2   0  long start2   0l  long total2   0l  boolean loop   true   start1   System currentTimeMillis    while  true      if  counter1    max        break      else       counter1          total1   System currentTimeMillis   - start1   start2   System currentTimeMillis    while  loop      switch  counter2        case max        loop   false        break      default        counter2          total2   System currentTimeMillis   - start2   System out println  While if else      total1    ms    System out println  Switch      total2    ms    System out println  Max Loops      max    System exit 0         Varying the loop count changes a lot    While if else  5ms Switch  1ms Max Loops  100000  While if else  5ms Switch  3ms Max Loops  1000000  While if else  5ms Switch  14ms Max Loops  10000000  While if else  5ms Switch  149ms Max Loops  100000000   add more statements if you want

User · Answer

The Switch  if only for readability  Giant if statements are harder to maintain and harder to read in my opinion    ERROR 01       intentional fall-through  or    ERROR 01    numError       The later is more error prone and requires more typing and formatting than the first

User · Answer

The Switch  if only for readability  Giant if statements are harder to maintain and harder to read in my opinion    ERROR 01       intentional fall-through  or    ERROR 01    numError       The later is more error prone and requires more typing and formatting than the first

User · Answer

Code for readability   If you want to know what performs better  use a profiler  as optimizations and compilers vary  and performance issues are rarely where people think they are

User · Answer

Compilers are really good at optimizing switch   Recent gcc is also good at optimizing a bunch of conditions in an if   I made some test cases on godbolt   When the case values are grouped close together  gcc  clang  and icc are all smart enough to use a bitmap to check if a value is one of the special ones   e g  gcc 5 2 -O3 compiles the switch to  and the if something very similar    errhandler switch errtype      gcc 5 2 -O3     cmpl     32   edi     ja   L5     movabsq  4301325442   rax     highest set bit is bit 32  the 33rd bit      btq  rdi   rax     jc   L10  L5      rep ret  L10      jmp fire special event     Notice that the bitmap is immediate data  so there s no potential data-cache miss accessing it  or a jump table   gcc 4 9 2 -O3 compiles the switch to a bitmap  but does the 1U lt  lt errNumber with mov shift   It compiles the if version to series of branches   errhandler switch errtype      gcc 4 9 2 -O3     leal    -1  rdi    ecx     cmpl     31   ecx      cmpl  32   edi  wouldn t have to wait an extra cycle for lea s output                  However  register read ports are limited on pre-SnB Intel     ja   L5     movl     1   eax     salq     cl   rax     with -march haswell  it will use BMI s shlx to avoid moving the shift count into ecx     testl    2150662721   eax     jne  L10  L5      rep ret  L10      jmp fire special event     Note how it subtracts 1 from errNumber  with lea to combine that operation with a move    That lets it fit the bitmap into a 32bit immediate  avoiding the 64bit-immediate movabsq which takes more instruction bytes   A shorter  in machine code  sequence would be       cmpl     32   edi     ja   L5     mov      2150662721   eax     dec      edi     movabsq and btq is fewer instructions   fewer Intel uops  but this saves several bytes     bt      edi   eax     jc  fire special event  L5      ret      The failure to use jc fire special event is omnipresent  and is a compiler bug    rep ret is used in branch targets  and following conditional branches  for the benefit of old AMD K8 and K10  pre-Bulldozer   What does  rep ret  mean    Without it  branch prediction doesn t work as well on those obsolete CPUs   bt  bit test  with a register arg is fast   It combines the work of left-shifting a 1 by errNumber bits and doing a test  but is still 1 cycle latency and only a single Intel uop   It s slow with a memory arg because of its way-too-CISC semantics  with a memory operand for the  bit string   the address of the byte to be tested is computed based on the other arg  divided by 8   and isn t limited to the 1  2  4  or 8byte chunk pointed to by the memory operand   From Agner Fog s instruction tables  a variable-count shift instruction is slower than a bt on recent Intel  2 uops instead of 1  and shift doesn t do everything else that s needed

User · Answer

When it comes to compiling the program  I don t know if there is any difference  But as for the program itself and keeping the code as simple as possible  I personally think it depends on what you want to do  if else if else statements have their advantages  which I think are   allow you to test a variable against specific ranges you can use functions  Standard Library or Personal  as conditionals    example    int a   cout lt  lt  enter value  n    cin gt  gt a    if  a  gt  0  amp  amp  a  lt  5            cout lt  lt  a is between 0  5 n        else if a  gt  5  amp  amp  a  lt  10        cout lt  lt  a is between 5 10 n        else           a is not an integer  or is not in range 0 10 n     However  If else if else statements can get complicated and messy  despite your best attempts  in a hurry  Switch statements tend to be clearer  cleaner  and easier to read  but can only be used to test against specific values  example    int a   cout lt  lt  enter value  n    cin gt  gt a    switch a         case 0      case 1      case 2       case 3      case 4      case 5          cout lt  lt  a is between 0 5 and equals    lt  lt a lt  lt   n           break        other case statements     default          cout lt  lt  a is not between the range or is not a good value n          break    I prefer if - else if - else statements  but it really is up to you  If you want to use functions as the conditions  or you want to test something against a range  array  or vector and or you don t mind dealing with the complicated nesting  I would recommend using If else if else blocks  If you want to test against single values or you want a clean and easy to read block  I would recommend you use switch   case blocks

User · Answer

If your cases are likely to remain grouped in the future--if more than one case corresponds to one result--the switch may prove to be easier to read and maintain

User · Answer

I would pick the if statement for the sake of clarity and convention  although I m sure that some would disagree  After all  you are wanting to do something if some condition is true  Having a switch with one action seems a little    unneccesary

User · Answer

For the special case that you ve provided in your example  the clearest code is probably   if  RequiresSpecialEvent numError       fire special event      Obviously this just moves the problem to a different area of the code  but now you have the opportunity to reuse this test   You also have more options for how to solve it   You could use std  set  for example   bool RequiresSpecialEvent int numError        return specialSet find numError     specialSet end        I m not suggesting that this is the best implementation of RequiresSpecialEvent  just that it s an option   You can still use a switch or if-else chain  or a lookup table  or some bit-manipulation on the value  whatever   The more obscure your decision process becomes  the more value you ll derive from having it in an isolated function

User · Answer

Seeing as you only have 30 error codes  code up your own jump table  then you make all optimisation choices yourself  jump will always be quickest   rather than hope the compiler will do the right thing  It also makes the code very small  apart from the static declaration of the jump table   It also has the side benefit that with a debugger you can modify the behaviour at runtime should you so need  just by poking the table data directly

User · Answer

Im not the person to tell you about speed and memory usage  but looking at a switch statment is a hell of a lot easier to understand then a large if statement  especially 2-3 months down the line

User · Answer

Compiler will optimise it anyway - go for the switch as it s the most readable

User · Answer

switch is definitely preferred   It s easier to look at a switch s list of cases  amp  know for sure what it is doing than to read the long if condition     The duplication in the if condition is hard on the eyes   Suppose one of the    was written     would you notice   Or if one instance of  numError  was written  nmuError   which just happened to compile   I d generally prefer to use polymorphism instead of the switch  but without more details of the context  it s hard to say   As for performance  your best bet is to use a profiler to measure the performance of your application in conditions that are similar to what you expect in the wild   Otherwise  you re probably optimizing in the wrong place and in the wrong way

User · Answer

I agree with the compacity of the switch solution but IMO you re hijacking the switch here  The purpose of the switch is to have different handling depending on the value  If you had to explain your algo in pseudo-code  you d use an if  because  semantically  that s what it is  if whatever error do this    So unless you intend someday to change your code to have specific code for each error  I would use if

User · Answer

They work equally well   Performance is about the same given a modern compiler   I prefer if statements over case statements because they are more readable  and more flexible -- you can add other conditions not based on numeric equality  like      max  lt  min     But for the simple case you posted here  it doesn t really matter  just do what s most readable to you

User · Answer

If your cases are likely to remain grouped in the future--if more than one case corresponds to one result--the switch may prove to be easier to read and maintain

User · Answer

Im not the person to tell you about speed and memory usage  but looking at a switch statment is a hell of a lot easier to understand then a large if statement  especially 2-3 months down the line

User · Answer

I would say use SWITCH  This way you only have to implement differing outcomes  Your ten identical cases can use the default  Should one change all you need to is explicitly implement the change  no need to edit the default  It s also far easier to add or remove cases from a SWITCH than to edit IF and ELSEIF   switch numerror       ERROR 20     fire special event      break      default     null    break      Maybe even test your condition  in this case numerror  against a list of possibilities  an array perhaps so your SWITCH isn t even used unless there definately will be an outcome

User · Answer

I agree with the compacity of the switch solution but IMO you re hijacking the switch here  The purpose of the switch is to have different handling depending on the value  If you had to explain your algo in pseudo-code  you d use an if  because  semantically  that s what it is  if whatever error do this    So unless you intend someday to change your code to have specific code for each error  I would use if

User · Answer

Compiler will optimise it anyway - go for the switch as it s the most readable

User · Answer

Compiler will optimise it anyway - go for the switch as it s the most readable

User · Answer

Use switch   In the worst case the compiler will generate the same code as a if-else chain  so you don t lose anything  If in doubt put the most common cases first into the switch statement   In the best case the optimizer may find a better way to generate the code  Common things a compiler does is to build a binary decision tree  saves compares and jumps in the average case  or simply build a jump-table  works without compares at all

User · Answer

Compilers are really good at optimizing switch   Recent gcc is also good at optimizing a bunch of conditions in an if   I made some test cases on godbolt   When the case values are grouped close together  gcc  clang  and icc are all smart enough to use a bitmap to check if a value is one of the special ones   e g  gcc 5 2 -O3 compiles the switch to  and the if something very similar    errhandler switch errtype      gcc 5 2 -O3     cmpl     32   edi     ja   L5     movabsq  4301325442   rax     highest set bit is bit 32  the 33rd bit      btq  rdi   rax     jc   L10  L5      rep ret  L10      jmp fire special event     Notice that the bitmap is immediate data  so there s no potential data-cache miss accessing it  or a jump table   gcc 4 9 2 -O3 compiles the switch to a bitmap  but does the 1U lt  lt errNumber with mov shift   It compiles the if version to series of branches   errhandler switch errtype      gcc 4 9 2 -O3     leal    -1  rdi    ecx     cmpl     31   ecx      cmpl  32   edi  wouldn t have to wait an extra cycle for lea s output                  However  register read ports are limited on pre-SnB Intel     ja   L5     movl     1   eax     salq     cl   rax     with -march haswell  it will use BMI s shlx to avoid moving the shift count into ecx     testl    2150662721   eax     jne  L10  L5      rep ret  L10      jmp fire special event     Note how it subtracts 1 from errNumber  with lea to combine that operation with a move    That lets it fit the bitmap into a 32bit immediate  avoiding the 64bit-immediate movabsq which takes more instruction bytes   A shorter  in machine code  sequence would be       cmpl     32   edi     ja   L5     mov      2150662721   eax     dec      edi     movabsq and btq is fewer instructions   fewer Intel uops  but this saves several bytes     bt      edi   eax     jc  fire special event  L5      ret      The failure to use jc fire special event is omnipresent  and is a compiler bug    rep ret is used in branch targets  and following conditional branches  for the benefit of old AMD K8 and K10  pre-Bulldozer   What does  rep ret  mean    Without it  branch prediction doesn t work as well on those obsolete CPUs   bt  bit test  with a register arg is fast   It combines the work of left-shifting a 1 by errNumber bits and doing a test  but is still 1 cycle latency and only a single Intel uop   It s slow with a memory arg because of its way-too-CISC semantics  with a memory operand for the  bit string   the address of the byte to be tested is computed based on the other arg  divided by 8   and isn t limited to the 1  2  4  or 8byte chunk pointed to by the memory operand   From Agner Fog s instruction tables  a variable-count shift instruction is slower than a bt on recent Intel  2 uops instead of 1  and shift doesn t do everything else that s needed

User · Answer

If your cases are likely to remain grouped in the future--if more than one case corresponds to one result--the switch may prove to be easier to read and maintain

User · Answer

If your cases are likely to remain grouped in the future--if more than one case corresponds to one result--the switch may prove to be easier to read and maintain

User · Answer

IMO this is a perfect example of what switch fall-through was made for

User · Answer

The Switch  if only for readability  Giant if statements are harder to maintain and harder to read in my opinion    ERROR 01       intentional fall-through  or    ERROR 01    numError       The later is more error prone and requires more typing and formatting than the first

User · Answer

switch is definitely preferred   It s easier to look at a switch s list of cases  amp  know for sure what it is doing than to read the long if condition     The duplication in the if condition is hard on the eyes   Suppose one of the    was written     would you notice   Or if one instance of  numError  was written  nmuError   which just happened to compile   I d generally prefer to use polymorphism instead of the switch  but without more details of the context  it s hard to say   As for performance  your best bet is to use a profiler to measure the performance of your application in conditions that are similar to what you expect in the wild   Otherwise  you re probably optimizing in the wrong place and in the wrong way

User · Answer

Compiler will optimise it anyway - go for the switch as it s the most readable

User · Answer

I would pick the if statement for the sake of clarity and convention  although I m sure that some would disagree  After all  you are wanting to do something if some condition is true  Having a switch with one action seems a little    unneccesary

User · Answer

IMO this is a perfect example of what switch fall-through was made for

User · Answer

I m not sure about best-practise  but I d use switch - and then trap intentional fall-through via  default

User · Answer

I m not sure about best-practise  but I d use switch - and then trap intentional fall-through via  default

User · Answer

The Switch  if only for readability  Giant if statements are harder to maintain and harder to read in my opinion    ERROR 01       intentional fall-through  or    ERROR 01    numError       The later is more error prone and requires more typing and formatting than the first

User · Answer

Aesthetically I tend to favor this approach   unsigned int special events           ERROR 01      ERROR 07      ERROR 0A      ERROR 10      ERROR 15      ERROR 16      ERROR 20      int special events length   sizeof  special events    sizeof  unsigned int     void process event unsigned int numError         for  int i   0  i  lt  special events length  i               if  numError    special events i                  fire special event                 break                           Make the data a little smarter so we can make the logic a little dumber   I realize it looks weird   Here s the inspiration  from how I d do it in Python    special events         ERROR 01      ERROR 07      ERROR 0A      ERROR 10      ERROR 15      ERROR 16      ERROR 20        def process event numError       if numError in special events           fire special event

User · Answer

IMO this is a perfect example of what switch fall-through was made for

User · Answer

They work equally well   Performance is about the same given a modern compiler   I prefer if statements over case statements because they are more readable  and more flexible -- you can add other conditions not based on numeric equality  like      max  lt  min     But for the simple case you posted here  it doesn t really matter  just do what s most readable to you

User · Answer

I m not sure about best-practise  but I d use switch - and then trap intentional fall-through via  default

User · Answer

I agree with the compacity of the switch solution but IMO you re hijacking the switch here  The purpose of the switch is to have different handling depending on the value  If you had to explain your algo in pseudo-code  you d use an if  because  semantically  that s what it is  if whatever error do this    So unless you intend someday to change your code to have specific code for each error  I would use if

User · Answer

IMO this is a perfect example of what switch fall-through was made for

User · Answer

They work equally well   Performance is about the same given a modern compiler   I prefer if statements over case statements because they are more readable  and more flexible -- you can add other conditions not based on numeric equality  like      max  lt  min     But for the simple case you posted here  it doesn t really matter  just do what s most readable to you

User · Answer

They work equally well   Performance is about the same given a modern compiler   I prefer if statements over case statements because they are more readable  and more flexible -- you can add other conditions not based on numeric equality  like      max  lt  min     But for the simple case you posted here  it doesn t really matter  just do what s most readable to you

User · Answer

Use switch   In the worst case the compiler will generate the same code as a if-else chain  so you don t lose anything  If in doubt put the most common cases first into the switch statement   In the best case the optimizer may find a better way to generate the code  Common things a compiler does is to build a binary decision tree  saves compares and jumps in the average case  or simply build a jump-table  works without compares at all

User · Answer

For the special case that you ve provided in your example  the clearest code is probably   if  RequiresSpecialEvent numError       fire special event      Obviously this just moves the problem to a different area of the code  but now you have the opportunity to reuse this test   You also have more options for how to solve it   You could use std  set  for example   bool RequiresSpecialEvent int numError        return specialSet find numError     specialSet end        I m not suggesting that this is the best implementation of RequiresSpecialEvent  just that it s an option   You can still use a switch or if-else chain  or a lookup table  or some bit-manipulation on the value  whatever   The more obscure your decision process becomes  the more value you ll derive from having it in an isolated function

[c++] Advantage of switch over if-else statement

Examples related to c++

Examples related to if-statement

Examples related to optimization

Examples related to switch-statement