退出函数

# include <stdio.h>
main()
{
    printf("hello, world\n");
}

打印终止状态

# gcc hello\ world.c
#./a.out
hello, world
# echo $? 
13

启动C99扩展

# gcc -std=c99 hello\ world.c 
hello world.c:3:1: warning: return type defaults to ‘int’ [enabled by default]
 main()
 ^
# ./a.out 
hello, world
# echo $?
0

函数atexit