在C中使用头文件 [英] Using header files in C

问题描述

我有我的 main.c >文件和 library.c （其中存储了所有函数）和 library.h （其中所有原型

在 main.c中我将 #include库.h但是当我尝试编译时，函数不能被识别。

我做错了什么？

我使用GCC构建文件。

test.c：
$ b

  #includelibrary .h
 
 int main（）
 {
 int num = 5; 
 sum（num）; 
} 
  

library.c

  #includelibrary.h
 
 
 int sum（int num）
 {
返回num + 5; 
} 
  

library.h

  #ifndef LIBRARY_H 
 #define LIBRARY_H 
 
 #include< stdio.h> 
 
 int sum（int num）; 
 
 #endif 
  

出错：

C：\ Users \Gabriel\Desktop\test.o：test.c ||未定义对`sum'的引用|

解决方案

包含头文件是不够的。头文件中的原型只是告诉编译器应该有一个函数。

您必须将该函数实际添加到程序中。这是在链接时完成的。最简单的方法是

$ g $ p $ g $ gcc -o myprog test.c library.c

还有更复杂的选项。如果您想要将多个文件实际添加到库中，则可以独立编译它们并构建存档。

  gcc -o library.o library.c 
 gcc -o someother.o someother.c 
 ar a libmy.a library.o someother.o 
 
 gcc -o myprog test.c -l my 
  

I'm having a couple of issues including custom libraries in my program

I have my main.c file and a library.c (where all the functions are stored) and library.h (where all the prototypes are stored).

In main.c I'm placing #include "library.h" but the functions don't get recognized when I try to compile.

Am I doing something wrong?

I'm using GCC to build the file.

test.c:

#include "library.h"

int main()
{
    int num = 5;
    sum(num);
}

library.c

#include "library.h"


int sum(int num)
{
    return num + 5;
}

library.h

#ifndef LIBRARY_H
#define LIBRARY_H

#include <stdio.h>

int sum(int num);

#endif

Getting error:

C:\Users\Gabriel\Desktop\test.o:test.c|| undefined reference to `sum'|

解决方案

Including the header file is not sufficient. The prototype in the header file just tells the compiler that there should be a function.

You have to actually add the function to the program. That is done when linking. the simplest way would be

gcc -o myprog test.c library.c

There are more sophisticated option. If you want to add several files actually to a library you can compile them independently and build the archive. Here are some commmands that show the basic idea.

gcc -o library.o library.c
gcc -o someother.o someother.c
ar a libmy.a library.o someother.o

gcc -o myprog test.c -l my

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