C语言 收到警告“隐式声明函数‘strlen’”
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Receiving warning "implicit declaration of function 'strlen'"
提问by Joe.Z
I have a some simple code, but I am receiving a warning:
我有一些简单的代码，但我收到警告：
-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'
The following is the code:
以下是代码：
#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);
......
The definition of strlen()is:
的定义strlen()是：
#include <string.h>
size_t strlen(const char *s);
how to get rid of this warning.
如何摆脱这个警告。
回答by sukhvir
it's #include <string.h>. You are spelling it wrong in your code. Also if you ever get that warning in your compiler .. always do man function_nameon terminal to see the header required for that function
它是#include <string.h>。您在代码中拼写错误。此外，如果您在编译器中收到该警告.. 总是man function_name在终端上查看该函数所需的标头
#include <string.h> // correct header
#include <strings.h> // incorrect header - change this in your code to string.h
回答by Shafik Yaghmour
You were bitten by a easy to make mistake, you included the posix strings.hheader:
你被一个容易犯的错误所困扰，你包含了posix strings.h头文件：
#include <strings.h>
instead of:
代替：
#include <string.h>
the posixheader includes support for:
的POSIX报头包括用于支持：
int bcmp(const void *, const void *, size_t); (LEGACY )
void bcopy(const void *, void *, size_t); (LEGACY )
void bzero(void *, size_t); (LEGACY )
int ffs(int);
char *index(const char *, int); (LEGACY )
char *rindex(const char *, int); (LEGACY )
int strcasecmp(const char *, const char *);
int strncasecmp(const char *, const char *, size_t);
which are all non-standard functions, this also explains the lack of error, I am having a hard time finding a good reference but BSDsystems version of strings.hused to also include string.h.
这些都是非标准函数，这也解释了没有错误的原因，我很难找到一个好的参考，但BSD系统版本的strings.h曾经也包含string.h。
回答by peterchaula
It turns out the code was #include <stdlib.h>and my output was :
原来代码是#include <stdlib.h>，我的输出是：
Solution:
解决方案：
Changed stdlib.hto stdio.hand the warning was gone
更改stdlib.h为stdio.h并且警告消失了
In short, the compiler is trying to tell you that it couldn't find the declaration of a function. This is a result of a). No header file included b) wrong header file name .eg" sring.h"
简而言之，编译器试图告诉您它找不到函数的声明。这是a)的结果。不包含头文件 b) 错误的头文件名。例如“sring.h”
