directory

  • A. __cplusplus profile
  • 2. __cplusplus is used
  • Guess you like it

C/C++ learning Directory >> C language basics

A. __cplusplus profile

__cplusplus and extern “C” are usually used in pairs, and we often see the __cplusplus keyword when reading programs, as in this code:

/ * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * / / / @ Author: programming ape said // @blog (personal Blog address): www.codersrc.com // @file :C language tutorial - C language __cplusplus //@Time:2021/07/14 07:30 //@Motto: No accumulation of small steps without a thousand miles, no accumulation of small streams without rivers and oceans, the wonderful life of the program needs to be unremitting accumulation!  /******************************************************************************************/ #ifndef __CODERSRC_H__ #define __CODERSRC_H__ #ifdef __cplusplus #define __dersrc_h__ #ifdef __cplusplus Instead of C + + extern "C" {# endif / *... * do something here *................................. */ #ifdef __cplusplus } #endif #endif /*end of __CODERSRC_H__*/Copy the code

The “# ifNdef __CODERSRC_H**, #define __CODERSRC_H**, #endif” macros are used to prevent the header from being referenced repeatedly.

It also tells the compiler that if __cplusplus is defined (CPP files define this macro by default), it should be compiled in C (that is, calling C in C ++).

Important note: this is mandatory if C++ is calling a third-party library written in CExtern “C”Tell the compiler to compile in C mode, otherwise there will be compilation error problem;

2. __cplusplus is used

/ * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * / / / @ Author: programming ape said // @blog (personal Blog address): www.codersrc.com // @file :C language tutorial - C language __cplusplus //@Time:2021/07/14 07:30 //@Motto: No accumulation of small steps without a thousand miles, no accumulation of small streams without rivers and oceans, the wonderful life of the program needs to be unremitting accumulation!  /******************************************************************************************/ #ifdef __cplusplus extern "C" { #endif void *memset(void* ,int , size_t); #ifdef __cplusplus } #endifCopy the code

Since C and C++ are different, it would be too much trouble to define two sets of header files in order to implement a program that is compatible with both C and C++, so __cplusplus is unique to C++. __cplusplus is actually C++. This is where the first code above is used. If this code appears in a C++ file, it will be compiled to read:

/ * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * / / / @ Author: programming ape said // @blog (personal Blog address): www.codersrc.com // @file :C language tutorial - C language __cplusplus //@Time:2021/07/14 07:30 //@Motto: No accumulation of small steps without a thousand miles, no accumulation of small streams without rivers and oceans, the wonderful life of the program needs to be unremitting accumulation!  / * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * / / * * * * * * * * * * conditional compilation in C + + files after the * * * * * * * * * * * * * * * / extern "C" {void * memset (void *, int, size_t); } in the C file, after a conditional compilation, this code becomes: / * * * * * * * * * * C file conditional compilation results after * * * * * * * * * * * * * / void * memset (void *, int, size_t);Copy the code

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C language __cplusplus

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