Range of values in C Int and Long 32 - 64 bits

Question

I m confused with range of values of Int variable in C   I know that a 32bits unsigned int have a range of  0 to 65 535  So long has 0 to 4 294 967 295  This is fine in 32bits machine  But now in 64bits machines all thing keep the same  Or maybe my int capacity is different   I understand this questions as newbie  but I m really confused   This method signature is not helping too      unsigned long long int atomicAdd unsigned long long int  address  unsigned long long int val

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No  int in C is not defined to be 32 bits  int and long are not defined to be any specific size at all  The only thing the language guarantees is that sizeof char  lt  sizeof short  lt  sizeof long     Theoretically a compiler could make short  char  and long all the same number of bits  I know of some that actually did that for all those types save char   This is why C now defines types like uint16 t and uint32 t  If you need a specific size  you are supposed to use one of those

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In C and C   you have these least requirements  i e actual implementations can have larger magnitudes   signed char  -2 07 1 to  2 07-1 short        -2 15 1 to  2 15-1 int          -2 15 1 to  2 15-1 long         -2 31 1 to  2 31-1 long long    -2 63 1 to  2 63-1   Now  on particular implementations  you have a variety of bit ranges  The wikipedia article describes this nicely

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There s no one answer   The standard defines minimum ranges   An int must be able to hold at least 65535   Most modern compilers however allow ints to be 32-bit values   Additionally  there s nothing preventing multiple types from having the same capacity  e g  int and long     That being said  the standard does say in your particular case   0    18446744073709551615   as the range for unsigned long long int   Further reading  http   en wikipedia org wiki C variable types and declarations Size

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Have a look at the limits h file in your system it will tell the system specific limits  Or check man limits h and go to the  Numerical Limits  section

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Excerpt from K amp R      short is often 16 bits  long 32 bits and int either 16 bits or   32 bits  Each compiler is free to choose appropriate sizes for its own   hardware  subject only to the restriction that shorts and ints are   at least 16 bits  longs are at least 32 bits  and short is no   longer than int  which is no longer than long      You can make use of limits h that contains the definition of the limits for the decimal float types    include  lt stdio h gt   include  lt stdlib h gt   include  lt limits h gt   include  lt float h gt    int main int argc  char   argv         printf  CHAR BIT         d n   CHAR BIT       printf  CHAR MAX         d n   CHAR MAX       printf  CHAR MIN         d n   CHAR MIN       printf  INT MAX          d n   INT MAX       printf  INT MIN          d n   INT MIN       printf  LONG MAX         ld n    long  LONG MAX       printf  LONG MIN         ld n    long  LONG MIN       printf  SCHAR MAX        d n   SCHAR MAX       printf  SCHAR MIN        d n   SCHAR MIN       printf  SHRT MAX         d n   SHRT MAX       printf  SHRT MIN         d n   SHRT MIN       printf  UCHAR MAX        d n   UCHAR MAX       printf  UINT MAX         u n    unsigned int  UINT MAX       printf  ULONG MAX        lu n    unsigned long  ULONG MAX       printf  USHRT MAX        d n    unsigned short  USHRT MAX       printf  FLT MAX          g n    float  FLT MAX       printf  FLT MIN          g n    float  FLT MIN       printf  -FLT MAX         g n    float  -FLT MAX       printf  -FLT MIN         g n    float  -FLT MIN       printf  DBL MAX          g n    double  DBL MAX       printf  DBL MIN          g n    double  DBL MIN       printf  -DBL MAX         g n    double  -DBL MAX        return  EXIT SUCCESS       Maybe you might have to tweak a little bit on your machine  but it is a good template to start to get an idea of the  implementation-defined  min and max values

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A 32-bit unsigned int has a range from 0 to 4 294 967 295  0 to 65535 would be a 16-bit unsigned   An unsigned long long  and  on a 64-bit implementation  possibly also ulong and possibly uint as well  have a range  at least  from 0 to 18 446 744 073 709 551 615  264-1   In theory it could be greater than that  but at least for now that s rare to nonexistent

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It is better to include stdlib h  Since without stdlibg it takes long as long

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In C  and C   memory requirements of some variable    signed char  -2 07 to  2 07-1   short        -2 15 to  2 15-1   int          -2 15 to  2 15-1   long         -2 31 to  2 31-1   long long    -2 63 to  2 63-1     signed char  -2 07 to  2 07-1   short        -2 15 to  2 15-1   int          -2 31 to  2 31-1   long         -2 31 to  2 31-1   long long    -2 63 to  2 63-1   depends on compiler and architecture of hardware  The international standard for the C language requires only that the size of short variables should be less than or equal to the size of type int  which in turn should be less than or equal to the size of type long

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In fact  unsigned int on most modern processors  ARM  Intel AMD  Alpha  SPARC  Itanium  PowerPC  will have a range of 0 to 2 32 - 1 which is 4 294 967 295   0xffffffff because int  both signed and unsigned  will be 32 bits long and the largest one is as stated    unsigned short will have maximal value 2 16 - 1   65 535     unsigned  long long int will have a length of 64 bits  long int will be enough under most 64 bit Linuxes  etc  but the standard promises 64 bits for long long int   Hence these have the range 0 to 2 64 - 1   18446744073709551615

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Take a look at limits h  You can find the specific values for your compiler  INT MIN and INT MAX will be of interest

[c] Range of values in C Int and Long 32 - 64 bits

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