c - 将 C 标准更改为 c99 后使用 UNIX time.h 时出错

Question

<分区>

Answer 1

作为man timeradd说，只有在定义了 _DEFAULT_SOURCE feature-test-macro 时，函数 timeradd 的定义才可用:

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

   All functions shown above:
       Since glibc 2.19:
           _DEFAULT_SOURCE
       Glibc 2.19 and earlier:
           _BSD_SOURCE

_DEFAULT_SOURCE 宏的描述 man feature_test_macros说:

This macro can be defined to ensure that the "default" definitions are provided even when the defaults would otherwise be disabled, as happens when individual macros are explicitly defined, or the compiler is invoked in one of its "standard" modes (e.g., cc -std=c99).

因此您需要明确定义 _DEFAULT_SOURCE 宏以使函数 timeradd 在 -std=c99 模式下可用:

#define _DEFAULT_SOURCE
#include <sys/time.h>
...
timeradd(...);