使用＃include< filename>和＃include< filename.h>在C ++？ [英] What is the difference between using #include<filename> and #include<filename.h> in C++?
问题描述
使用＃include< filename>和 C ++ 中的＃include< filename.h >？
What is the difference between using #include<filename> and #include<filename.h> in C++? Which of the two is used and why is it is used?
推荐答案
C ++只包含在C标准中找不到的文件使用 filename.h 。自从第一个C ++标准出来（1998），他们使用 filename 为自己的头。
C++ only include-files not found in the C standard never used filename.h . Since the very first C++ Standard came out (1998) they have used filename for their own headers.
C标准继承的文件变为 cfilename ，而不是 filename.h 。使用像 filename.h 的继承的C文件已被弃用，但仍是C ++标准的一部分。
Files inherited by the C Standard became cfilename instead of filename.h. The C files inherited used like filename.h are deprecated, but still part of the C++ standard.
不同之处在于C中未定义为宏的名称位于<$ c中的命名空间 std :: $ c> cfilename ，而 filename.h 中的名称位于全局命名空间范围内。所以你会在cstddef中找到stddef.h中的 :: size_t 和 std :: size_t 。两者都是标准C ++，但是使用:: size_t已被弃用（见C ++标准的附录D）。
The difference is that names not defined as macros in C are found within namespace std:: in cfilename in C++, while names in filename.h are within the global namespace scope. So you will find ::size_t in stddef.h, and std::size_t in cstddef. Both are Standard C++, but use of ::size_t is deprecated (See Annex D of the C++ Standard).
现在这些是不同的。
- 编译器
- 与非常旧的C ++编译器的兼容性
- 名称位于命名空间
std ::中。没有名称冲突了。 - 新的C ++功能（例如float，long的重载数学函数）
- C兼容性标题（
filename.h）可能会在将来消失。
- Names are within namespace
std::. No name-clashes anymore. - New C++ features (e.g. overloaded math functions for float, long)
- C Compatibility Headers (
filename.h) could disappear in future.
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