使用头文件时出现未定义的符号错误 [英] Undefined symbols error when using a header file

问题描述

我遇到以下错误，无法终生发现自己在做错什么.

I'm getting the following error and can't for the life of me figure out what I'm doing wrong.

$ gcc main.c -o main

Undefined symbols:
  "_wtf", referenced from:
      _main in ccu2Qr2V.o
ld: symbol(s) not found
collect2: ld returned 1 exit status

main.c:

#include <stdio.h>
#include "wtf.h"

main(){
    wtf();
}

wtf.h:

void wtf();

wtf.c:

void wtf(){
    printf("I never see the light of day.");
}

现在，如果我将整个函数包括在头文件中，而不仅仅是签名，它就可以正常工作，所以我知道其中包括了wtf.h.为什么编译器看不到wtf.c?还是我错过了什么?

Now, if I include the entire function in the header file instead of just the signature, it complies fine so I know wtf.h is being included. Why doesn't the compiler see wtf.c? Or am I missing something?

致谢.

推荐答案

您需要将wtf与您的main链接.一起编译的最简单方法-gcc将为您链接'em，如下所示:

You need to link wtf with your main. Easiest way to compile it together - gcc will link 'em for you, like this:

gcc main.c wtf.c -o main

更长的方式(wtf的单独编译):

Longer way (separate compilation of wtf):

gcc -c wtf.c
gcc main.c wtf.o -o main

更长(单独的编译和链接)

Even longer (separate compilation and linking)

gcc -c wtf.c
gcc -c main.c
gcc main.o wtf.o -o main

您可以直接运行ld，而不会影响上一个gcc调用.

Instead of last gcc call you can run ld directly with the same effect.

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