动态链接库嵌套样例

foo2.c

int foo2 = 20;
void foo2_func() {}

foo1.c

extern int foo2;
int foo1 = 10;
int dummy = 20;

void foo1_func()
{
    int a = foo2;
    int b = dummy;
    int c = foo1;

    foo2_func();
}

main.c

#include <stdlib.h>
extern int foo1;
extern int foo1;
int a[2048];
int dummy = 10;

void main()
{
    char *m = malloc(1024);
    foo1 = 5;

    foo1_func();
    while(1)sleep(1000);
}

运行j结果：

jiaming@jiaming-pc:~/Documents/test/libso$ gcc -shared -fPIC -o libf2.so foo2.c
jiaming@jiaming-pc:~/Documents/test/libso$ gcc -shared -fPIC -o libf1.so foo1.c -L. -lf2
foo1.c: In function ‘foo1_func’:
foo1.c:11:5: warning: implicit declaration of function ‘foo2_func’; did you mean ‘foo1_func’? [-Wimplicit-function-declaration]
     foo2_func();
     ^~~~~~~~~
     foo1_func
jiaming@jiaming-pc:~/Documents/test/libso$ gcc -o hello main.c -L. -lf1
main.c: In function ‘main’:
main.c:12:5: warning: implicit declaration of function ‘foo1_func’ [-Wimplicit-function-declaration]
     foo1_func();
     ^~~~~~~~~
main.c:13:13: warning: implicit declaration of function ‘sleep’ [-Wimplicit-function-declaration]
     while(1)sleep(1000);
             ^~~~~
/usr/bin/ld: warning: libf2.so, needed by ./libf1.so, not found (try using -rpath or -rpath-link)
/usr/bin/ld: ./libf1.so: undefined reference to `foo2'
/usr/bin/ld: ./libf1.so: undefined reference to `foo2_func'
collect2: error: ld returned 1 exit status
jiaming@jiaming-pc:~/Documents/test/libso$ export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:.
jiaming@jiaming-pc:~/Documents/test/libso$ gcc -o hello main.c -L. -lf1
main.c: In function ‘main’:
main.c:12:5: warning: implicit declaration of function ‘foo1_func’ [-Wimplicit-function-declaration]
     foo1_func();
     ^~~~~~~~~
main.c:13:13: warning: implicit declaration of function ‘sleep’ [-Wimplicit-function-declaration]
     while(1)sleep(1000);
             ^~~~~
jiaming@jiaming-pc:~/Documents/test/libso$ ./hello 
^C

1. 动态库在制作的时候，亦可结合其它动态库。
2. -I（注意是大写的i）给gcc添加自定义的头文件的路径，​​-Imyinclude​​。
3. -L 给gcc添加额外的搜索库的路径。
4. -l （小写L）参数就是用来指定程序要链接的库，-l参数紧接着就是库名，数学库文件名是libm.so，很容易看出，把库文件名的头lib和尾.so去掉就是库名了，​​lm​​。