iostream为什么包含time.h? [英] Why does iostream include time.h?

问题描述

考虑以下代码:

#include <iostream>

template<class C>
struct time { };

int main() { }

它产生(GCC 4.5):

It produces (GCC 4.5):

error: ‘template<class C> struct time’ redeclared as different kind of symbol
/usr/include/time.h:186:15: error: previous declaration of ‘time_t time(time_t*)’

1. 为什么iostream包含time_t time(time_t*)?
2. 为什么iostream在std名称空间之外包含time_t time(time_t*)?
3. (未答复)为什么删除template<class C>不会收到此错误?

1. Why does iostream include time_t time(time_t*) ?
2. Why does iostream include time_t time(time_t*) outside std namespace?
3. (unanswered) Why, if I remove template<class C>, do I not get this error?

推荐答案

如果运行g++ -H -Wall -c testim.cc(其中testim.cc是示例)，则会看到

If you run g++ -H -Wall -c testim.cc (where testim.cc is your example) you'll see that

.... /usr/include/c++/4.6/bits/ios_base.h
..... /usr/include/c++/4.6/ext/atomicity.h
...... /usr/include/c++/4.6/x86_64-linux-gnu/./bits/gthr.h
....... /usr/include/c++/4.6/x86_64-linux-gnu/./bits/gthr-default.h
........ /usr/include/pthread.h
......... /usr/include/sched.h
.......... /usr/lib/gcc/x86_64-linux-gnu/4.6/include/stddef.h
.......... /usr/include/time.h

因此，包含了<time.h>以获得pthread支持.

So <time.h> is included for pthread support.

这与Debian/Sid/AMD64上的GCC 4.6一起使用

This is with GCC 4.6 on Debian/Sid/AMD64

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