implicit declaration of function is invalid in c99

回答:当出现"implicit declaration of function is invalid in c99"的警告时，通常是因为在主程序中没有将函数声明的头文件包含进来。编译器会在编译时发出警告，提示函数的隐式声明无效。你可以检查一下是否正确包含了函数声明的头文件。在你提供的代码中，注释掉了#include "key.h"这一行，可能就是缺少了这个头文件导致的警告。在检查头文件是否正确包含进来之后，你可以再次编译代码，看看是否还会出现这个警告。如果问题仍然存在，可以考虑检查其他函数的声明和定义，确保所有文件的位置都在同一个文件夹中。希望这些信息对你有帮助。<span class="em">1</span><span class="em">2</span><span class="em">3</span>
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