c - 收到警告 "implicit declaration of function ' strlen'"

Question

我有一些简单的代码，但我收到了警告:

-bash-3.2$ gcc -Wall print_process_environ.c -o p_p
print_process_environ.c: In function 'print_process_environ':
print_process_environ.c:24: warning: implicit declaration of function 'strlen'
print_process_environ.c:24: warning: incompatible implicit declaration of built-in function 'strlen'

代码如下:

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <strings.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <fcntl.h>
#include <strings.h>

    void
    print_process_environ(pid_t pid)
    {
        int     fd;
        char    filename[24];
        char    environ[1024];
        size_t  length;
        char    *next_var;

        snprintf(filename, sizeof(filename), "/proc/%d/environ", (int)pid);
        printf("length of filename: %d\n", strlen(filename));

        fd = open(filename, O_RDONLY);
......

strlen()的定义是:

   #include <string.h>

   size_t strlen(const char *s);

如何摆脱这个警告。

Answer 1

是#include <string.h> .您在代码中拼写错误。另外，如果您在编译器中收到该警告.. 总是做 man function_name在终端上查看该功能所需的 header

 #include <string.h> // correct header
 #include <strings.h> // incorrect header - change this in your code to string.h