在Visual Studio 2008中，它默认为__int64，除非你定义了_USE_32BIT_TIME_T。最好是假装不知道它的定义，因为它可以(也将)在不同平台之间改变。

您可以使用typeid来找出time_t在您的系统中是如何定义的。

#include <iostream> // cout
#include <ctime>    // time_t
#include <typeinfo> // typeid, name

using namespace std;

int main()
{
    cout << "Test 1: The type of time_t is: \t\t" 
         << typeid(time_t).name() << endl;
    cout << "Test 2: time_t is a signed long?: \t"
         << (typeid(time_t) == typeid(signed long) ? "true" : "false") << endl;
    cout << "Test 3: time_t is an unsigned long?: \t" 
         << (typeid(time_t) == typeid(unsigned long) ? "true" : "false") << endl;
    return 0;
}

在我的系统中，输出是:

Test 1: The type of time_t is:          l
Test 2: time_t is a signed long?:       true
Test 3: time_t is an unsigned long?:    false

在Visual Studio 2008中，它默认为__int64，除非你定义了_USE_32BIT_TIME_T。最好是假装不知道它的定义，因为它可以(也将)在不同平台之间改变。

[根]#猫时间

#include <time.h>

int main(int argc, char** argv)
{
        time_t test;
        return 0;
}

[root]# gcc -E time.c | grep __time_t .c

类型定义long int __time_t;

它在$INCDIR/bits/types.h中定义:

# 131 "/usr/include/bits/types.h" 3 4
# 1 "/usr/include/bits/typesizes.h" 1 3 4
# 132 "/usr/include/bits/types.h" 2 3 4

time_t类型定义最终是什么?

健壮的代码并不关心类型是什么。

C物种time_t为实类型，如double, long long, int64_t, int等。

它甚至可以是无符号的，因为许多时间函数的返回值表明错误不是-1，而是(time_t)(-1) -这种实现选择并不常见。

关键是“需要知道”的类型很少。代码的编写应该避免这种需要。

然而，当代码想要打印原始time_t时，会出现一个常见的“需要知道的问题”。转换为最宽的整数类型将适应大多数现代情况。

time_t now = 0;
time(&now);
printf("%jd", (intmax_t) now);
// or 
printf("%lld", (long long) now);

转换为双精度或长双精度也可以，但可能提供不精确的十进制输出

printf("%.16e", (double) now);

time_t维基百科的文章给出了一些解释。归根结底，在C规范中，time_t的类型是不保证的。

The time_t datatype is a data type in the ISO C library defined for storing system time values. Such values are returned from the standard time() library function. This type is a typedef defined in the standard header. ISO C defines time_t as an arithmetic type, but does not specify any particular type, range, resolution, or encoding for it. Also unspecified are the meanings of arithmetic operations applied to time values. Unix and POSIX-compliant systems implement the time_t type as a signed integer (typically 32 or 64 bits wide) which represents the number of seconds since the start of the Unix epoch: midnight UTC of January 1, 1970 (not counting leap seconds). Some systems correctly handle negative time values, while others do not. Systems using a 32-bit time_t type are susceptible to the Year 2038 problem.