什么时候.h不需要包含头文件? [英] When is .h not needed to include a header file?
问题描述
这样做:
#include< iostream>
using namespace std;
但此操作失败:
#include< stdio>
不需要 .h
/ p>
关于命名空间问题,我没有在 cstdio
中找到这样的逻辑:
#pragma once
#ifndef _CSTDIO_
#define _CSTDIO_
#include< yvals.h>
#ifdef _STD_USING
#undef _STD_USING
#include< stdio.h>
#define _STD_USING
#else / * _STD_USING * /
#include< stdio.h>
#endif / * _STD_USING * /
// undef常用宏覆盖
#undef clearerr
#undef feof
#undef ferror
#undef getc
#undef getchar
#undef putc
#undef putchar
#define _HAS_CONVENTIONAL_CLIB 1
#define _IOBASE _base
#define _IOPTR _ptr
#define _IOCNT _cnt
#ifndef _FPOSOFF
#define _FPOSOFF(fp)((long)(fp))
#endif / * _FPOSOFF *
typedef FILE _Filet;
#ifndef RC_INVOKED
#if _GLOBAL_USING
_STD_BEGIN
使用:: _ Filet;
使用:: size_t; using :: fpos_t; using :: FILE;
using :: clearerr; using :: fclose;使用:: feof;
using :: ferror;使用:: fflush; using :: fgetc;
using :: fgetpos; using :: fgets; using :: fopen;
using :: fprintf;使用:: fputc; using :: fputs;
using :: fread; using :: freopen;使用:: fscanf;
using :: fseek; using :: fsetpos;使用:: ftell;
using :: fwrite; using :: getc; using :: getchar;
using :: gets; using :: perror;
using :: putc;使用:: putchar;
using :: printf;使用:: puts; using :: remove;
using :: rename; using :: rewind; using :: scanf;
using :: setbuf; using :: setvbuf;使用:: sprintf;
using :: sscanf;使用:: tmpfile;使用:: tmpnam;
using :: ungetc; using :: vfprintf; using :: vprintf;
using :: vsprintf;
_STD_END
#endif / * _GLOBAL_USING * /
#endif / * RC_INVOKED * /
#endif / * _CSTDIO_ *
标准,其中没有一个具有.h扩展名。 stdio.h
的C ++版本是:
#include< cstdio>包含 stdio.h
的
在C ++ std
命名空间中的名称,
,但是如果你愿意,你仍然可以使用C ++代码中的所有C标准头文件。
编辑:将名称放在cstdio的GCC版本中的std命名空间中的宏是:
_GLIBCXX_BEGIN_NAMESPACE(std)
头文件通过尝试使用类似的方法做它应该做的:
std :: printf(hello);
。
This works:
#include <iostream>
using namespace std;
but this fails:
#include <stdio>
When is .h
not needed?
About the namespace issue,I didn't find such logic in cstdio
:
#pragma once
#ifndef _CSTDIO_
#define _CSTDIO_
#include <yvals.h>
#ifdef _STD_USING
#undef _STD_USING
#include <stdio.h>
#define _STD_USING
#else /* _STD_USING */
#include <stdio.h>
#endif /* _STD_USING */
// undef common macro overrides
#undef clearerr
#undef feof
#undef ferror
#undef getc
#undef getchar
#undef putc
#undef putchar
#define _HAS_CONVENTIONAL_CLIB 1
#define _IOBASE _base
#define _IOPTR _ptr
#define _IOCNT _cnt
#ifndef _FPOSOFF
#define _FPOSOFF(fp) ((long)(fp))
#endif /* _FPOSOFF */
typedef FILE _Filet;
#ifndef RC_INVOKED
#if _GLOBAL_USING
_STD_BEGIN
using ::_Filet;
using ::size_t; using ::fpos_t; using ::FILE;
using ::clearerr; using ::fclose; using ::feof;
using ::ferror; using ::fflush; using ::fgetc;
using ::fgetpos; using ::fgets; using ::fopen;
using ::fprintf; using ::fputc; using ::fputs;
using ::fread; using ::freopen; using ::fscanf;
using ::fseek; using ::fsetpos; using ::ftell;
using ::fwrite; using ::getc; using ::getchar;
using ::gets; using ::perror;
using ::putc; using ::putchar;
using ::printf; using ::puts; using ::remove;
using ::rename; using ::rewind; using ::scanf;
using ::setbuf; using ::setvbuf; using ::sprintf;
using ::sscanf; using ::tmpfile; using ::tmpnam;
using ::ungetc; using ::vfprintf; using ::vprintf;
using ::vsprintf;
_STD_END
#endif /* _GLOBAL_USING */
#endif /* RC_INVOKED */
#endif /* _CSTDIO_ */
It's not needed for the header files defined by the C++ Standard, none of which have a .h extension. The C++ version of stdio.h
is:
#include <cstdio>
which wraps stdio.h
, placing the names in it in the C++ std
namespace,
but you can still use all the C Standard header files in C++ code, if you wish.
Edit: The macro that places the names in the std namespace in the GCC version of cstdio is:
_GLIBCXX_BEGIN_NAMESPACE(std)
You can check that your own header does what it should do by trying to use something like:
std::printf( "hello" );
in your code.
这篇关于什么时候.h不需要包含头文件?的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!