C C check if one bit is set in i e int variable

Question

int temp   0x5E     in binary 0b1011110    Is there such a way to check if bit 3 in temp is 1 or 0 without bit shifting and masking   Just want to know if there is some built in function for this  or am I forced to write one myself

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Use std  bitset   include  lt bitset gt   include  lt iostream gt   int main         int temp   0x5E      std  bitset lt sizeof int  CHAR BITS gt    bits temp           0 - gt  bit 1        2 - gt  bit 3     std  cout  lt  lt  bits 2   lt  lt  std  endl

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I make this   LATGbits LATG0   m amp 0x8  0     to check if  bit-2 of m is 1

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There is  namely the  bittest intrinsic instruction

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Why not use something as simple as this   uint8 t status   255  cout  lt  lt   binary      for  int i   sizeof status  8 -1   i gt -1  i--      if   status  amp   1  lt  lt  i            cout  lt  lt   1          else         cout  lt  lt   0           OUTPUT  binary  11111111

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define CHECK BIT var pos    var gt  gt pos   amp  1    pos - Bit position strarting from 0   returns 0 or 1

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While it is quite late to answer now  there is a simple way one could find if Nth bit is set or not  simply using POWER and MODULUS mathematical operators   Let us say we want to know if  temp  has Nth bit set or not  The following boolean expression will give true if bit is set  0 otherwise      temp MODULUS 2 N 1    2 N     Consider the following example    int temp   0x5E     in binary 0b1011110      BIT 0 is LSB   If I want to know if 3rd bit is set or not  I get    94 MODULUS 16    14   2 3   So expression returns true  indicating 3rd bit is set

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The precedent answers show you how to handle bit checks  but more often then not  it is all about flags encoded in an integer  which is not well defined in any of the precedent cases  In a typical scenario  flags are defined as integers themselves  with a bit to 1 for the specific bit it refers to  In the example hereafter  you can check if the integer has ANY flag from a list of flags  multiple error flags concatenated  or if EVERY flag is in the integer  multiple success flags concatenated   Following an example of how to handle flags in an integer  Live example available here  https   rextester com XIKE82408   g    7 4 0   include  lt iostream gt   include  lt stdint h gt   inline bool any flag present unsigned int value  unsigned int flags        return bool value  amp  flags      inline bool all flags present unsigned int value  unsigned int flags        return  value  amp  flags     flags     enum  unsigned int       ERROR 1   1U      ERROR 2   2U     or 0b10     ERROR 3   4U     or 0b100     SUCCESS 1   8U      SUCCESS 2   16U      OTHER FLAG   32U      int main void        unsigned int value   0b101011     ERROR 1  ERROR 2  SUCCESS 1  OTHER FLAG     unsigned int all error flags   ERROR 1   ERROR 2   ERROR 3      unsigned int all success flags   SUCCESS 1   SUCCESS 2           std  cout  lt  lt   quot Was there at least one error   quot   lt  lt  any flag present value  all error flags   lt  lt  std  endl      std  cout  lt  lt   quot Are all success flags enabled   quot   lt  lt  all flags present value  all success flags   lt  lt  std  endl      std  cout  lt  lt   quot Is the other flag enabled with eror 1   quot   lt  lt  all flags present value  ERROR 1   OTHER FLAG   lt  lt  std  endl      return 0

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According to this description of bit-fields  there is a method for defining and accessing fields directly  The example in this entry goes   struct preferences       unsigned int likes ice cream   1      unsigned int plays golf   1      unsigned int watches tv   1      unsigned int reads books   1       struct preferences fred   fred likes ice cream   1  fred plays golf   1  fred watches tv   1  fred reads books   0   if  fred likes ice cream    1                  Also  there is a warning there      However  bit members in structs have practical drawbacks  First  the ordering of bits in memory is architecture dependent and memory padding rules varies from compiler to compiler  In addition  many popular compilers generate inefficient code for reading and writing bit members  and there are potentially severe thread safety issues relating to bit fields  especially on multiprocessor systems  due to the fact that most machines cannot manipulate arbitrary sets of bits in memory  but must instead load and store whole words

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i was trying to read a 32-bit integer which defined the flags for an object in PDFs and this wasn t working for me  what fixed it was changing the define    define CHECK BIT var pos    var  amp   1  lt  lt  pos       1  lt  lt  pos     the operand  amp  returns an integer with the flags that both have in 1  and it wasn t casting properly into boolean  this did the trick

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I would just use a std  bitset if it s C    Simple  Straight-forward  No chance for stupid errors   typedef std  bitset lt sizeof int  gt  IntBits  bool is set   IntBits value  test position     or how about this silliness  template lt unsigned int Exp gt  struct pow 2       static const unsigned int value   2   pow 2 lt Exp-1 gt   value      template lt  gt  struct pow 2 lt 0 gt        static const unsigned int value   1      template lt unsigned int Pos gt  bool is bit set unsigned int value        return  value  amp  pow 2 lt Pos gt   value     0      bool result   is bit set lt 2 gt  value

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What the selected answer is doing is actually wrong  The below function will return the bit position or 0 depending on if the bit is actually enabled  This is not what the poster was asking for    define CHECK BIT var pos    var   amp   1 lt  lt  pos      Here is what the poster was originally looking for  The below function will return either a 1 or 0 if the bit is enabled and not the position    define CHECK BIT var pos     var  gt  gt  pos    amp  1

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the fastest way seems to be a lookup table for masks

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One approach will be checking within the following condition   if    mask  gt  gt  bit    amp  1    An explanation program will be    include  lt stdio h gt   unsigned int bitCheck unsigned int mask  int pin    int main void      unsigned int mask   6      6   0110    int pin0   0     int pin1   1     int pin2   2     int pin3   3     unsigned int bit0  bitCheck  mask  pin0      unsigned int bit1  bitCheck  mask  pin1      unsigned int bit2  bitCheck  mask  pin2      unsigned int bit3  bitCheck  mask  pin3       printf  Mask    d    gt  gt   0110 n   mask       if   bit0    1          printf  Pin  d is Set n   pin0       else        printf  Pin  d is not Set n   pin0             if   bit1    1          printf  Pin  d is Set n   pin1       else        printf  Pin  d is not Set n   pin1            if   bit2    1          printf  Pin  d is Set n   pin2       else        printf  Pin  d is not Set n   pin2            if   bit3    1          printf  Pin  d is Set n   pin3       else        printf  Pin  d is not Set n   pin3           unsigned int bitCheck unsigned int mask  int bit      if    mask  gt  gt  bit    amp  1         return 1      else        return 0           Output    Mask   6    gt  gt   0110 Pin 0 is not Set Pin 1 is Set Pin 2 is Set Pin 3 is not Set

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fast and best macro  define get bit status        YOUR VAR   amp      1  lt  lt  BITX           if  get rx pin status        1  lt  lt  BITX          do

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Why all these bit shifting operations and need for library functions   If you have the value the OP posted  1011110 and you want to know if the bit in the 3rd position from the right is set  just do  int temp   0b1011110  if  temp  amp  4        or  temp  amp  0b0100  if that s how you roll      DoSomething     Or  something that may be more easily interpreted by future readers of the code with no  include needed  int temp   0b1011110   Bool bThirdBitIsSet    temp  amp  4    1   0  if  bThirdBitIsSet     DoSomething     Or if you like it to look a bit prettier   include  lt stdbool h gt  int temp   0b1011110  bool bThirdBitIsSet    temp  amp  4    true   false  if  bThirdBitIsSet     DoSomething

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Yeah  I know I don t  have  to do it this way   But I usually write          Return type  8 16 32 64 int size  is specified by argument size     template lt class TYPE gt  inline TYPE BIT const TYPE  amp  x    return TYPE 1   lt  lt  x     template lt class TYPE gt  inline bool IsBitSet const TYPE  amp  x  const TYPE  amp  y    return 0     x  amp  y       E g    IsBitSet  foo  BIT 3    BIT 6         Checks if Bit 3 OR 6 is set    Amongst other things  this approach    Accommodates 8 16 32 64 bit integers  Detects IsBitSet int32 int64  calls without my knowledge  amp  consent  Inlined Template  so no function calling overhead  const amp  references  so nothing needs to be duplicated copied   And we are guaranteed that the compiler will pick up any typo s that attempt to change the arguments  0   makes the code more clear  amp  obvious   The primary point to writing code is always to communicate clearly and efficiently with other programmers  including those of lesser skill  While not applicable to this particular case    In general  templated functions avoid the issue of evaluating arguments multiple times   A known problem with some  define macros    E g    define ABS X     X  lt 0    -  X     X     nbsp    nbsp    nbsp  ABS i

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For the low-level x86 specific solution use the x86 TEST opcode   Your compiler should turn  bittest into this though

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You can use a Bitset - http   www cppreference com wiki stl bitset start

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I use this    define CHECK BIT var pos       var   amp   pos    gt  0      1     0      where  pos  is defined as 2 n  i g  1 2 4 8 16 32       Returns    1 if true  0 if false

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Check if bit N  starting from 0  is set   temp  amp   1  lt  lt  N    There is no builtin function for this

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You could  simulate  shifting and masking  if  0x5e  2 2 2   2

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if you just want a real hard coded way     define IS BIT3 SET var      var   amp  0x04     0x04     note this hw dependent and assumes this bit order 7654 3210 and var is 8 bit    include  stdafx h   define IS BIT3 SET var      var   amp  0x04     0x04   int  tmain int argc   TCHAR  argv          int temp  0x5E      printf    d  n   IS BIT3 SET temp        temp   0x00      printf    d  n   IS BIT3 SET temp        temp   0x04      printf    d  n   IS BIT3 SET temp        temp   0xfb      printf    d  n   IS BIT3 SET temp        scanf  waitng  d   amp temp        return 0      Results in   1 0 1 0

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In C  if you want to hide bit manipulation  you can write a macro    define CHECK BIT var pos    var   amp   1 lt  lt  pos      and use it this way to check the nth bit from the right end   CHECK BIT temp  n - 1    In C    you can use std  bitset

[c++] C/C++ check if one bit is set in, i.e. int variable

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