Correct use of PRID64 in C + + (reprint)

Transferred from: http://blog.csdn.net/win_lin/article/details/7912693

　　

Example reference high-performance streaming media server Srs:https://github.com/winlinvip/simple-rtmp-server

The PRID64 is widely used in SRS to achieve 32 and 64-bit systems common.

C + + uses PRID64, which takes two steps:

1. Contains header files:<inttypes.h>
2. Define macros: __stdc_format_macros, you can add-d__stdc_format_macros at compile time, or define this macro before you include a file.

The int64_t is used to represent a 64-bit integer, a long long int in a 32-bit system, and a long int in a 64-bit system, so the format method for printing int64_t is:

    printf ("%ld"//  64bit OS      printf ("%lld " // 32bit OS  

Of course there are cross-platform approaches:

#include <inttypes.h>printf ("%"PRId64"\ n", value); //equivalent to 64 bits:printf"%" "LD" "\ n", value); //or 32-bit:printf"%" "LLD" "\ n", value);

where printf ("abc" "DEF" "Ghi") writes multiple strings in such a way that there is no problem.

But, anyway compile, the error is: error:expected ') ' Before ' PRId64 '

Look for the definition of this macro,/usr/include/inttypes.h:

    /*The ISO C99 standard specifies, these macros must only be defined if explicitly requested. */      #if!defined __cplusplus | | Defined __stdc_format_macros          # if__wordsize = = -# define __pri64_prefix"L"# define __priptr_prefix"L"      # Else# define __pri64_prefix"ll"# define __priptr_prefix # endif/*Macros for printing format specifiers. */            /*Decimal notation. */# define PRID8"D"# define PRID16"D"# define PRID32"D"# define PRID64 __pri64_prefix"D"  

Originally this is defined for C use, C + + to use it, it is necessary to define a __stdc_format_macros macro display to open it.

    /*test_int64.cpp g++-d__stdc_format_macros-o test_int64-g-o0 test_int64.cpp*/#include<stdio.h>#include<inttypes.h>intMainintargcChar**argv) {int64_t value=0xFFFFFFFFFFFF; printf ("int64_t=%"PRId64", sizeof (int64_t) =%d\n", Value,sizeof(int64_t)); }  

Compile and execute:

g++-d__stdc_format_macros-o test_int64-g-o0 test_int64.cpp

./test_int64

int64_t=281474976710655, sizeof (int64_t) =8

For the new C + + standard-std=c++0x, you can also use a better way:

    /*test_int64_1.cpp g++-o test_int64_1-g-o0 test_int64_1.cpp*/#include<stdio.h>#include<cinttypes>using namespacestd; intMainintargcChar**argv) {int64_t value=0xFFFFFFFFFFFF; printf ("int64_t=%"PRId64", sizeof (int64_t) =%d\n", Value,sizeof(int64_t)); }  

Do not define the macro, compile and execute:

g++-o test_int64_1-g-o0 test_int64_1.cpp-std=c++0x

./test_int64_1

int64_t=281474976710655, sizeof (int64_t) =8

Of course, you have to specify a new parameter:-std=c++0x, otherwise it will error "#error this file requires compiler and library support for the upcoming ISO C + + standard, C + + 0x. This currently experimental, and must are enabled with the-std=c++0x or-std=gnu++0x compiler options. "

If you can compile with newer g++, you can use the latter, otherwise you can define macros directly with the former.

Correct use of PRID64 in C + + (reprint)