Question

我在程序中使用clock_gettime。我试过包括但是没有效果。我还在编译器参数中添加了-lrt但仍然遇到了相同的错误。

这是

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);
               ^

生成文件

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>

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Answer 1

在包含标题（<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将定义公开为如下：

  ·  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).

Answer 2

如果可以使用以下链接器和编译器标志

CFLAGS  = -g -Wall -std=c99 -D_POSIX_SOURCE -D_GNU_SOURCE
LDFLAGS = -lpthread -lrt

您可以在Linux系统中完成构建。 -lrt链接器和-D_POSIX_SOURCE是重要的链接

Answer 3

只需将-std = c99替换为-std = gnu99。这样，您不必添加_POSIX_C_SOURCE

clock_gettime和CLOCK_MONOTONIC上的编译错误

3 个答案: