C language: 7. How to use C language multi source files

1、 Example 1： Multiple source file examples

A larger project should not write all the code in the same file , It is usually divided into several documents . Therefore, you need to compile multiple files .
Example 1 Introduced the use of gcc Command to compile multiple files

1、 Define function source file /hello.c

#include <stdio.h>

int main() {
    
    int maxNum = max(33,20);
    printf("the max value is %d", maxNum);
    return 0;
}

2、 Define function source file /max.c

int max(int n1, int n2)
{
    
    if(n1 > n2){
    
        return n1;
    } else{
    
        return n2;
    }
}

3、 compiling

linux Environmental use gcc Command compilation main.out Executable file , And implement
gcc max.c hello.c -o main.out
The results are as follows

2、 Compile infrequently changed files in advance

Because if the whole project is compiled, it will be very slow , Therefore, it is generally possible to compile infrequently changed files directly into .o file ;
As an example 1 Documents in hello.c、max.c You can use the following method , Improve compilation speed .

1、 Compile infrequently changed files

gcc -c max.c max.o

The compiled file is not executable

2、 take main The entry and the compiled .o Compile files together

Compile the file
gcc max.o hello.c
Execute the compiled executable

2、

3、 Example of separation of header file and function definition

If multiple people cooperate in the development , If other colleagues want to use the code I wrote , Header files can be declared （.h） The return value of the function 、 The parameter type is written .

In this way, he only has .o In the case of documents , Also know how to use the function I wrote .

1、 Define header file /include/factorial.h

Declare the function in the header file

#ifndef INC_3_FACTORIAL_H
#define INC_3_FACTORIAL_H
unsigned int Factorial(unsigned int n);
unsigned int FactorialByIteration(unsigned int n);
#endif //INC_3_FACTORIAL_H

2、 Define source code file /src/factorial.c

Implement functions in the source file

#include "../include/factorial.h"
unsigned int Factorial(unsigned int n) {
    
    if( n == 0){
    
        return 1;
    } else{
    
        return n * Factorial( n - 1);
    }
}

3、 stay /main.c Call in

#include <stdio.h>
#include "include/factorial.h"
int main() {
    
    //puts("hello world");
    printf("3 != %d\n", Factorial(2));
    return 0;
}

4、cmake Add compiler in /CMakelists.txt

cmake_minimum_required(VERSION 3.20)
project(3 C)

set(CMAKE_C_STANDARD 99)

add_executable(3 main.c src/factorial.c)

5、 Execute the compiled file