函数隐式声明警告如何解决

When compiling a C program you might find that the compiler gives you a warning similar to

编译C程序时，您可能会发现编译器向您发出类似于以下内容的警告

hello.c:6:3: warning: implicitly declaring library function
      'printf' with type 'int (const char *, ...)'
      [-Wimplicit-function-declaration]
  printf("Name length: %u", length);
  ^

or

要么

hello.c:5:16: warning: implicitly declaring library function
      'strlen' with type 'unsigned long (const char *)'
      [-Wimplicit-function-declaration]
  int length = strlen(name);
               ^

This problem occurs because you used a function from the standard library without first including the appropriate header file.

发生此问题的原因是您使用了标准库中的函数而没有首先包含相应的头文件。

The compiler will also give you a suggestion, like the following one:

编译器还会给您一个建议，如下所示：

hello.c:5:16: note: include the header <string.h> or
      explicitly provide a declaration for 'strlen'

which points you in the right direction.

指出正确的方向。

In this case, adding

在这种情况下，添加

#include <stdio.h>

cs