clock_gettime和CLOCK_MONOTONIC上的编译错误

Question

我在程序中使用clock_gettime.我试过包括但是没有效果.我还为我的编译器参数添加了-lrt但仍然得到相同的错误.

这是开启

CentOS Linux release 7.2.1511 (Core)
gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-4)
GNU ld version 2.23.52.0.1-55.el7 20130226
ldd (GNU libc) 2.17

编译器输出:

gcc -o main packet.c connect.c transport.c accept.c main.c close.c util.c receive.c send.c congestion.c -Wall -g -std=c99 -lrt
util.c: In function ‘millis’:
util.c:42:21: error: storage size of ‘t’ isn’t known
     struct timespec t;
                     ^
util.c:43:5: warning: implicit declaration of function ‘clock_gettime’ [-Wimplicit-function-declaration]
     clock_gettime(CLOCK_MONOTONIC_RAW, &t);
     ^
util.c:43:19: error: ‘CLOCK_MONOTONIC_RAW’ undeclared (first use in this function)
     clock_gettime(CLOCK_MONOTONIC_RAW, &t);
               ^

Makefile文件

CFLAGS = -Wall -g -std=c99
LIBS = -lrt

# Should be equivalent to your list of C files, if you don't build selectively
SRC=$(wildcard *.c)

main: $(SRC)
    gcc -o $@ $^ $(CFLAGS) $(LIBS)

util.h的顶部

#ifndef UTILS_438_H_
#define UTILS_438_H_

#include "const.h"
#include "data.h"
#include "transport.h"

#include <time.h>

util.c的顶部

#include "util.h"

#include <time.h>
#include <stdio.h>
#include <string.h>

如果我能提供更多信息以帮助解答这个问题,请告诉我

Answer 1

在包含header(<time.h>)之前,请执行

#define _POSIX_C_SOURCE 199309L

http://man7.org/linux/man-pages/man2/clock_gettime.2.html

glibc的功能测试宏要求(参见feature_test_macros(7)):

   clock_getres(), clock_gettime(), clock_settime():
          _POSIX_C_SOURCE >= 199309L

http://man7.org/linux/man-pages/man7/feature_test_macros.7.html

_POSIX_C_SOURCE定义此宏会导致头文件公开定义,如下所示:

  ·  The value 1 exposes definitions conforming to POSIX.1-1990 and
     ISO C (1990).

  ·  The value 2 or greater additionally exposes definitions for
     POSIX.2-1992.

  ·  The value 199309L or greater additionally exposes definitions
     for POSIX.1b (real-time extensions).

  ·  The value 199506L or greater additionally exposes definitions
     for POSIX.1c (threads).

  ·  (Since glibc 2.3.3) The value 200112L or greater additionally
     exposes definitions corresponding to the POSIX.1-2001 base
     specification (excluding the XSI extension).  This value also
     causes C95 (since glibc 2.12) and C99 (since glibc 2.10)
     features to be exposed (in other words, the equivalent of
     defining _ISOC99_SOURCE).

  ·  (Since glibc 2.10) The value 200809L or greater additionally
     exposes definitions corresponding to the POSIX.1-2008 base
     specification (excluding the XSI extension).