Definition of int64 t

Question

I am new to C C    so I have a couple of questions about a basic type    a  Can you explain to me the difference between int64 t and long  long int    In my understanding  both are 64 bit integers  Is there any reason to choose one over the other   b  I tried to look up the definition of int64 t on the web  without much success  Is there an authoritative source I need to consult for such questions   c  For code using int64 t to compile  I am currently including  lt iostream gt   which doesn t make much sense to me  Are there other includes that provide a declaration of int64 t

User · Answer

int64 t is typedef you can find that in  lt stdint h gt  in C

User · Answer

An int64 t should be 64 bits wide on any platform  hence the name   whereas a long can have different lengths on different platforms  In particular  sizeof long  is often 4  ie  32 bits

User · Answer

My 2 cents  from a current implementation Point of View and for SWIG users on k8  x86 64  architecture   Linux  First long long and long int are different types but sizeof long long     sizeof long int     sizeof int64 t   Gcc  First try to find where and how the compiler define int64 t and uint64 t  grepc -rn  typedef  INT64 TYPE   lib gcc  lib gcc x86 64-linux-gnu 9 include stdint-gcc h 43 typedef   INT64 TYPE   int64 t   lib gcc x86 64-linux-gnu 9 include stdint-gcc h 55 typedef   UINT64 TYPE   uint64 t    So we need to find this compiler macro definition  gcc -dM -E -x c  dev null   grep   INT64                   define   INT64 C c  c    L  define   INT64 MAX   0x7fffffffffffffffL  define   INT64 TYPE   long int  gcc -dM -E -x c    dev null   grep   INT64  define   INT64 C c  c    L  define   INT64 MAX   0x7fffffffffffffffL  define   INT64 TYPE   long int   Clang  clang -dM -E -x c    dev null   grep INT64 TYPE  define   INT64 TYPE   long int  define   UINT64 TYPE   long unsigned int   Clang  GNU compilers  -dM dumps a list of macros  -E prints results to stdout instead of a file  -x c and -x c   select the programming language when using a file without a filename extension  such as  dev null  Ref  https   web archive org web 20190803041507 http   nadeausoftware com articles 2011 12 c c tip how list compiler predefined macros  note  for swig user  on Linux x86 64 use -DSWIGWORDSIZE64  MacOS  On Catalina 10 15 IIRC  Clang  clang -dM -E -x c    dev null   grep INT64 TYPE  define   INT64 TYPE   long long int  define   UINT64 TYPE   long long unsigned int   Clang  -dM dumps a list of macros  -E prints results to stdout instead of a file  -x c and -x c   select the programming language when using a file without a filename extension  such as  dev null  Ref  https   web archive org web 20190803041507 http   nadeausoftware com articles 2011 12 c c tip how list compiler predefined macros  note  for swig user  on macOS x86 64 don t use -DSWIGWORDSIZE64  Visual Studio 2019  First sizeof long int     4 and sizeof long long     8  in stdint h we have    if  VCRT COMPILER PREPROCESSOR  typedef signed char        int8 t  typedef short              int16 t  typedef int                int32 t  typedef long long          int64 t  typedef unsigned char      uint8 t  typedef unsigned short     uint16 t  typedef unsigned int       uint32 t  typedef unsigned long long uint64 t    note  for swig user  on windows x86 64 don t use -DSWIGWORDSIZE64  SWIG Stuff  First see  https   github com swig swig blob 3a329566f8ae6210a610012ecd60f6455229fe77 Lib stdint i L20-L24 so you can control the typedef using SWIGWORDSIZE64 but     now the bad  SWIG Java and SWIG CSHARP do not take it into account  So you may want to use   if defined SWIGJAVA   if defined SWIGWORDSIZE64   define PRIMITIVE TYPEMAP NEW TYPE  TYPE   clear NEW TYPE   clear NEW TYPE     clear NEW TYPE  amp    clear const NEW TYPE  amp    apply TYPE   NEW TYPE     apply TYPE     NEW TYPE       apply TYPE  amp    NEW TYPE  amp      apply const TYPE  amp    const NEW TYPE  amp      enddef    PRIMITIVE TYPEMAP PRIMITIVE TYPEMAP long int  long long   PRIMITIVE TYPEMAP unsigned long int  long long    undef PRIMITIVE TYPEMAP  endif    defined SWIGWORDSIZE64   endif    defined SWIGJAVA    and   if defined SWIGCSHARP   if defined SWIGWORDSIZE64   define PRIMITIVE TYPEMAP NEW TYPE  TYPE   clear NEW TYPE   clear NEW TYPE     clear NEW TYPE  amp    clear const NEW TYPE  amp    apply TYPE   NEW TYPE     apply TYPE     NEW TYPE       apply TYPE  amp    NEW TYPE  amp      apply const TYPE  amp    const NEW TYPE  amp      enddef    PRIMITIVE TYPEMAP PRIMITIVE TYPEMAP long int  long long   PRIMITIVE TYPEMAP unsigned long int  unsigned long long    undef PRIMITIVE TYPEMAP  endif    defined SWIGWORDSIZE64   endif    defined SWIGCSHARP    So int64 t aka long int will be bind to Java C  long on Linux

User · Answer

a  Can you explain to me the difference between int64 t and long  long int   In my understanding  both are 64 bit integers  Is there any reason to choose one over the other    The former is a signed integer type with exactly 64 bits  The latter is a signed integer type with at least 32 bits      b  I tried to look up the definition of int64 t on the web  without much success  Is there an authoritative source I need to consult for such questions    http   cppreference com covers this here  http   en cppreference com w cpp types integer  The authoritative source  however  is the C   standard  this particular bit can be found in   18 4 Integer types  cstdint        c  For code using int64 t to compile  I am including  lt iostream gt   which doesn t make much sense to me  Are there other includes that provide a declaration of int64 t    It is declared in  lt cstdint gt  or  lt cinttypes gt   under namespace std   or in  lt stdint h gt  or  lt inttypes h gt   in the global namespace

User · Answer

int64 t is guaranteed by the C99 standard to be exactly 64 bits wide on platforms that implement it  there s no such guarantee for a long which is at least 32 bits so it could be more        7 18 1 3 Exact-width integer types 1 The typedef name intN t   designates a signed integer type with width N   no padding  bits  and   a two   s complement representation  Thus  int8 t denotes a signed   integer   type with a width of exactly 8 bits

[c++] Definition of int64_t

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