How do I convert a double into a string in C

Question

I need to store a double as a string   I know I  can use printf if I wanted to display it  but I just want to store it in a string variable so that I can store it in a map later  as the value  not the key

User · Answer

If you use C    avoid sprintf  It s un-C  y and has several problems  Stringstreams are the method of choice  preferably encapsulated as in Boost LexicalCast which can be done quite easily   template  lt typename T gt  std  string to string T const amp  value        stringstream sstr      sstr  lt  lt  value      return sstr str        Usage   string s   to string 42 5

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You can convert any thing to anything using this function   template lt class T   std  string  class U gt  T to U a        std  stringstream ss      T ret      ss  lt  lt  a      ss  gt  gt  ret      return ret       usage    std  string str   to 2 5   double d   to lt double gt   2 5

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If you use C    avoid sprintf  It s un-C  y and has several problems  Stringstreams are the method of choice  preferably encapsulated as in Boost LexicalCast which can be done quite easily   template  lt typename T gt  std  string to string T const amp  value        stringstream sstr      sstr  lt  lt  value      return sstr str        Usage   string s   to string 42 5

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The Standard C  11 way  if you don t care about the output format     include  lt string gt   auto str   std  to string 42 5      to string is a new library function introduced in N1803  r0   N1982  r1  and N2408  r2   Simple Numeric Access   There are also the stod function to perform the reverse operation    If you do want to have a different output format than   f   use the snprintf or ostringstream methods as illustrated in other answers

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sprintf is okay  but in C    the better  safer  and also slightly slower way of doing the conversion is with stringstream    include  lt sstream gt   include  lt string gt      In some function  double d   453 23  std  ostringstream os  os  lt  lt  d  std  string str   os str      You can also use Boost LexicalCast    include  lt boost lexical cast hpp gt   include  lt string gt      In some function  double d   453 23  std  string str   boost  lexical cast lt string gt  d     In both instances  str should be  453 23  afterward  LexicalCast has some advantages in that it ensures the transformation is complete  It uses stringstreams internally

User · Answer

The problem with lexical cast is the inability to define precision   Normally if you are converting a double to a string  it is because you want to print it out   If the precision is too much or too little  it would affect your output

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Herb Sutter has an excellent article on string formatting   I recommend reading it   I ve linked it before on SO

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Heh  I just wrote this  unrelated to this question    string temp       stringstream outStream  double ratio    currentImage- gt width 1 0f  currentImage- gt height  outStream  lt  lt    R     lt  lt  ratio  temp   outStream str        rest of the code

User · Answer

Take a look at sprintf   and family

User · Answer

The boost  tm  way   std  string str   boost  lexical cast lt std  string gt  dbl     The Standard C   way   std  ostringstream strs  strs  lt  lt  dbl  std  string str   strs str      Note  Don t forget  include  lt sstream gt

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Normaly for this operations you have to use the ecvt  fcvt or gcvt Functions      gcvt example     include  lt stdio h gt   include  lt stdlib h gt   main        char buffer  20     gcvt  1365 249 6 buffer     puts  buffer     gcvt  1365 249 3 buffer     puts  buffer     return 0     Output  1365 25 1 37e 003      As a Function   void double to char double f char   buffer     gcvt f 10 buffer

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The C way  char buffer 32   snprintf buffer  sizeof buffer     g   myDoubleVar       The C  03 way  std  ostringstream sstream  sstream  lt  lt  myDoubleVar  std  string varAsString   sstream str        The C  11 way  std  string varAsString   std  to string myDoubleVar       The boost way  std  string varAsString   boost  lexical cast lt std  string gt  myDoubleVar

User · Answer

You may want to read my prior posting on SO    Macro ed version with a temporary ostringstream object    For the record   In my own code  I favor snprintf     With a char array on the local stack  it s not that inefficient    Well  maybe if you exceeded the array size and looped to do it twice       I ve also wrapped it via vsnprintf     But that costs me some type checking   Yelp if you want the code

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You could try a more compact style   std  string number in string   double number in double   std  ostringstream output   number in string    dynamic cast lt  std  ostringstream  gt   amp  output  lt  lt  number in double  lt  lt   std  endl   - gt str

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Heh  I just wrote this  unrelated to this question    string temp       stringstream outStream  double ratio    currentImage- gt width 1 0f  currentImage- gt height  outStream  lt  lt    R     lt  lt  ratio  temp   outStream str        rest of the code

User · Answer

The boost  tm  way   std  string str   boost  lexical cast lt std  string gt  dbl     The Standard C   way   std  ostringstream strs  strs  lt  lt  dbl  std  string str   strs str      Note  Don t forget  include  lt sstream gt

User · Answer

sprintf is okay  but in C    the better  safer  and also slightly slower way of doing the conversion is with stringstream    include  lt sstream gt   include  lt string gt      In some function  double d   453 23  std  ostringstream os  os  lt  lt  d  std  string str   os str      You can also use Boost LexicalCast    include  lt boost lexical cast hpp gt   include  lt string gt      In some function  double d   453 23  std  string str   boost  lexical cast lt string gt  d     In both instances  str should be  453 23  afterward  LexicalCast has some advantages in that it ensures the transformation is complete  It uses stringstreams internally

User · Answer

Normaly for this operations you have to use the ecvt  fcvt or gcvt Functions      gcvt example     include  lt stdio h gt   include  lt stdlib h gt   main        char buffer  20     gcvt  1365 249 6 buffer     puts  buffer     gcvt  1365 249 3 buffer     puts  buffer     return 0     Output  1365 25 1 37e 003      As a Function   void double to char double f char   buffer     gcvt f 10 buffer

User · Answer

sprintf is okay  but in C    the better  safer  and also slightly slower way of doing the conversion is with stringstream    include  lt sstream gt   include  lt string gt      In some function  double d   453 23  std  ostringstream os  os  lt  lt  d  std  string str   os str      You can also use Boost LexicalCast    include  lt boost lexical cast hpp gt   include  lt string gt      In some function  double d   453 23  std  string str   boost  lexical cast lt string gt  d     In both instances  str should be  453 23  afterward  LexicalCast has some advantages in that it ensures the transformation is complete  It uses stringstreams internally

User · Answer

Take a look at sprintf   and family

User · Answer

The C way  char buffer 32   snprintf buffer  sizeof buffer     g   myDoubleVar       The C  03 way  std  ostringstream sstream  sstream  lt  lt  myDoubleVar  std  string varAsString   sstream str        The C  11 way  std  string varAsString   std  to string myDoubleVar       The boost way  std  string varAsString   boost  lexical cast lt std  string gt  myDoubleVar

User · Answer

Herb Sutter has an excellent article on string formatting   I recommend reading it   I ve linked it before on SO

User · Answer

You may want to read my prior posting on SO    Macro ed version with a temporary ostringstream object    For the record   In my own code  I favor snprintf     With a char array on the local stack  it s not that inefficient    Well  maybe if you exceeded the array size and looped to do it twice       I ve also wrapped it via vsnprintf     But that costs me some type checking   Yelp if you want the code

User · Answer

You could try a more compact style   std  string number in string   double number in double   std  ostringstream output   number in string    dynamic cast lt  std  ostringstream  gt   amp  output  lt  lt  number in double  lt  lt   std  endl   - gt str

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Use to string    example        include  lt iostream gt      include  lt string gt     using namespace std  int main          string pi    pi is     to string 3 1415926       cout lt  lt   pi     lt  lt  pi  lt  lt  endl     return 0      run it yourself   http   ideone com 7ejfaU These are available as well     string to string  int val   string to string  long val   string to string  long long val   string to string  unsigned val   string to string  unsigned long val   string to string  unsigned long long val   string to string  float val   string to string  double val   string to string  long double val

User · Answer

Herb Sutter has an excellent article on string formatting   I recommend reading it   I ve linked it before on SO

User · Answer

The problem with lexical cast is the inability to define precision   Normally if you are converting a double to a string  it is because you want to print it out   If the precision is too much or too little  it would affect your output

User · Answer

You can use std  to string in C  11  double d   3 0  std  string str   std  to string d

User · Answer

Use to string    example        include  lt iostream gt      include  lt string gt     using namespace std  int main          string pi    pi is     to string 3 1415926       cout lt  lt   pi     lt  lt  pi  lt  lt  endl     return 0      run it yourself   http   ideone com 7ejfaU These are available as well     string to string  int val   string to string  long val   string to string  long long val   string to string  unsigned val   string to string  unsigned long val   string to string  unsigned long long val   string to string  float val   string to string  double val   string to string  long double val

User · Answer

If you use C    avoid sprintf  It s un-C  y and has several problems  Stringstreams are the method of choice  preferably encapsulated as in Boost LexicalCast which can be done quite easily   template  lt typename T gt  std  string to string T const amp  value        stringstream sstr      sstr  lt  lt  value      return sstr str        Usage   string s   to string 42 5

User · Answer

Heh  I just wrote this  unrelated to this question    string temp       stringstream outStream  double ratio    currentImage- gt width 1 0f  currentImage- gt height  outStream  lt  lt    R     lt  lt  ratio  temp   outStream str        rest of the code

User · Answer

You could also use stringstream

User · Answer

You could also use stringstream

User · Answer

The C way  char buffer 32   snprintf buffer  sizeof buffer     g   myDoubleVar       The C  03 way  std  ostringstream sstream  sstream  lt  lt  myDoubleVar  std  string varAsString   sstream str        The C  11 way  std  string varAsString   std  to string myDoubleVar       The boost way  std  string varAsString   boost  lexical cast lt std  string gt  myDoubleVar

User · Answer

I would look at the C   String Toolkit Libary   Just posted a similar answer elsewhere   I have found it very fast and reliable    include  lt strtk hpp gt   double pi   M PI  std  string pi as string    strtk  type to string lt double gt   pi

User · Answer

Herb Sutter has an excellent article on string formatting   I recommend reading it   I ve linked it before on SO

User · Answer

You may want to read my prior posting on SO    Macro ed version with a temporary ostringstream object    For the record   In my own code  I favor snprintf     With a char array on the local stack  it s not that inefficient    Well  maybe if you exceeded the array size and looped to do it twice       I ve also wrapped it via vsnprintf     But that costs me some type checking   Yelp if you want the code

User · Answer

If you use C    avoid sprintf  It s un-C  y and has several problems  Stringstreams are the method of choice  preferably encapsulated as in Boost LexicalCast which can be done quite easily   template  lt typename T gt  std  string to string T const amp  value        stringstream sstr      sstr  lt  lt  value      return sstr str        Usage   string s   to string 42 5

User · Answer

Take a look at sprintf   and family

User · Answer

You may want to read my prior posting on SO    Macro ed version with a temporary ostringstream object    For the record   In my own code  I favor snprintf     With a char array on the local stack  it s not that inefficient    Well  maybe if you exceeded the array size and looped to do it twice       I ve also wrapped it via vsnprintf     But that costs me some type checking   Yelp if you want the code

User · Answer

The boost  tm  way   std  string str   boost  lexical cast lt std  string gt  dbl     The Standard C   way   std  ostringstream strs  strs  lt  lt  dbl  std  string str   strs str      Note  Don t forget  include  lt sstream gt

User · Answer

The boost  tm  way   std  string str   boost  lexical cast lt std  string gt  dbl     The Standard C   way   std  ostringstream strs  strs  lt  lt  dbl  std  string str   strs str      Note  Don t forget  include  lt sstream gt

User · Answer

You could also use stringstream

User · Answer

You can convert any thing to anything using this function   template lt class T   std  string  class U gt  T to U a        std  stringstream ss      T ret      ss  lt  lt  a      ss  gt  gt  ret      return ret       usage    std  string str   to 2 5   double d   to lt double gt   2 5

User · Answer

I would look at the C   String Toolkit Libary   Just posted a similar answer elsewhere   I have found it very fast and reliable    include  lt strtk hpp gt   double pi   M PI  std  string pi as string    strtk  type to string lt double gt   pi

User · Answer

sprintf is okay  but in C    the better  safer  and also slightly slower way of doing the conversion is with stringstream    include  lt sstream gt   include  lt string gt      In some function  double d   453 23  std  ostringstream os  os  lt  lt  d  std  string str   os str      You can also use Boost LexicalCast    include  lt boost lexical cast hpp gt   include  lt string gt      In some function  double d   453 23  std  string str   boost  lexical cast lt string gt  d     In both instances  str should be  453 23  afterward  LexicalCast has some advantages in that it ensures the transformation is complete  It uses stringstreams internally

User · Answer

Heh  I just wrote this  unrelated to this question    string temp       stringstream outStream  double ratio    currentImage- gt width 1 0f  currentImage- gt height  outStream  lt  lt    R     lt  lt  ratio  temp   outStream str        rest of the code

User · Answer

You can use std  to string in C  11  double d   3 0  std  string str   std  to string d

User · Answer

The Standard C  11 way  if you don t care about the output format     include  lt string gt   auto str   std  to string 42 5      to string is a new library function introduced in N1803  r0   N1982  r1  and N2408  r2   Simple Numeric Access   There are also the stod function to perform the reverse operation    If you do want to have a different output format than   f   use the snprintf or ostringstream methods as illustrated in other answers

User · Answer

You could also use stringstream

User · Answer

The C way  char buffer 32   snprintf buffer  sizeof buffer     g   myDoubleVar       The C  03 way  std  ostringstream sstream  sstream  lt  lt  myDoubleVar  std  string varAsString   sstream str        The C  11 way  std  string varAsString   std  to string myDoubleVar       The boost way  std  string varAsString   boost  lexical cast lt std  string gt  myDoubleVar

User · Answer

Take a look at sprintf   and family

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