目录
- 进程退出的形式
- 进程退出的几种方法
进程退出的形式
进程退出的几种情况
- 正常退出（自愿，代码运行完其结果正确）
- 错误退出（自愿，代码运行完其结果不正确）
- 异常退出（非自愿，代码异常直接终止）
- 被其他进程终止（非自愿）
自愿退出会返回一个退出码，由父进程接收。
在Linux上可以使用命令echo $?显示最近一次退出的进程返回的退出码
//现有如下代码，源文件名为mycode.c
# include <stdio.h>
int main(void)
{
printf("i am testing\n");
return 0;
}
运行以上代码……
使用命令echo $?显示退出码
正常退出的退出码为0，错误退出的退出码为非0
退出码反应了进程退出的原因。所以有必要知道这些退出码究竟代表着什么。
strerror（）函数的作用就是以字符的形式返回退出码。
//所在头文件 <string.h> //函数原型 char* strerror(int errNum);
//可以使用下面代码查看退出码对应的信息
# include <stdio.h>
# include <string.h>
int main(void)
{
for(int i = 0; i < 135; i++)
{
printf("%d: %s\n", i, strerror(i));
}
return 0;
}
Linux系统上一共有134个退出码，退出码“134”就已经不认识它了。
0: Success
1: Operation not permitted
2: No such file or directory
3: No such process
4: Interrupted system call
5: Input/output error
6: No such device or address
7: Argument list too long
8: Exec format error
9: Bad file descriptor
10: No child processes
11: Resource temporarily unavailable
12: Cannot allocate memory
13: Permission denied
14: Bad address
15: Block device required
16: Device or resource busy
17: File exists
18: Invalid cross-device link
19: No such device
20: Not a directory
21: Is a directory
22: Invalid argument
23: Too many open files in system
24: Too many open files
25: Inappropriate ioctl for device
26: Text file busy
27: File too large
28: No space left on device
29: Illegal seek
30: Read-only file system
31: Too many links
32: Broken pipe
33: Numerical argument out of domain
34: Numerical result out of range
35: Resource deadlock avoided
36: File name too long
37: No locks available
38: Function not implemented
39: Directory not empty
40: Too many levels of symbolic links
41: Unknown error 41
42: No message of desired type
43: Identifier removed
44: Channel number out of range
45: Level 2 not synchronized
46: Level 3 halted
47: Level 3 reset
48: Link number out of range
49: Protocol driver not attached
50: No CSI structure available
51: Level 2 halted
52: Invalid exchange
53: Invalid request descriptor
54: Exchange full
55: No anode
56: Invalid request code
57: Invalid slot
58: Unknown error 58
59: Bad font file format
60: Device not a stream
61: No data available
62: Timer expired
63: Out of streams resources
64: Machine is not on the network
65: Package not installed
66: Object is remote
67: Link has been severed
68: Advertise error
69: Srmount error
70: Communication error on send
71: Protocol error
72: Multihop attempted
73: RFS specific error
74: Bad message
75: Value too large for defined data type
76: Name not unique on network
77: File descriptor in bad state
78: Remote address changed
79: Can not access a needed shared library
80: Accessing a corrupted shared library
81: .lib section in a.out corrupted
82: Attempting to link in too many shared libraries
83: Cannot exec a shared library directly
84: Invalid or incomplete multibyte or wide character
85: Interrupted system call should be restarted
86: Streams pipe error
87: Too many users
88: Socket operation on non-socket
89: Destination address required
90: Message too long
91: Protocol wrong type for socket
92: Protocol not available
93: Protocol not supported
94: Socket type not supported
95: Operation not supported
96: Protocol family not supported
97: Address family not supported by protocol
98: Address already in use
99: Cannot assign requested address
100: Network is down
101: Network is unreachable
102: Network dropped connection on reset
103: Software caused connection abort
104: Connection reset by peer
105: No buffer space available
106: Transport endpoint is already connected
107: Transport endpoint is not connected
108: Cannot send after transport endpoint shutdown
109: Too many references: cannot splice
110: Connection timed out
111: Connection refused
112: Host is down
113: No route to host
114: Operation already in progress
115: Operation now in progress
116: Stale file handle
117: Structure needs cleaning
118: Not a XENIX named type file
119: No XENIX semaphores available
120: Is a named type file
121: Remote I/O error
122: Disk quota exceeded
123: No medium found
124: Wrong medium type
125: Operation canceled
126: Required key not available
127: Key has expired
128: Key has been revoked
129: Key was rejected by service
130: Owner died
131: State not recoverable
132: Operation not possible due to RF-kill
133: Memory page has hardware error
134: Unknown error 134
Linux上一切皆为文件，指令也是一个文件，当使用不存在的指令时，就会出现报错信息。
其退出码为2，退出码2代表的含义为： No such file or directory(没有这样的文件或目录)
进程退出的几种方法
正常终止的3种方法：
- main函数返回
- 调用exit
- 调用_exit
最常见的进程终止莫过于main函数返回了！需要注意main函数中返回才是进程退出，而非main函数返回并不能正常终止进程，只是函数返回。
【调用exit】
//所在头文件 #include <stdlib.h> //exit函数原型 void exit(int status);
exit函数是语言层面的函数，是对系统调用函数_exit的封装。
它可以在main函数中调用，也可以在非main函数中调用，都可以达到终止进程的目的。
C标准还规定了两个宏EXIT_SUCCESS和EXIT_FAILURE可以作为exit的参数，用来指示这个进程是正常退出还是错误退出。
# include <stdio.h>
# include <string.h>
# include <stdlib.h>
int main(void)
{
printf("i am testing\n");
exit(EXIT_SUCCESS);
return 0;
}
# include <stdio.h>
# include <string.h>
# include <stdlib.h>
int main(void)
{
printf("i am testing\n");
exit(EXIT_FAILURE); //修改exit函数的参数
return 0;
}
【调用_exit函数】
//所在头文件 #include <unistd.h> //_exit函数原型 void _exit(int status);
_exit是系统调用函数。_exit函数的本质就是调用了系统调用函数_exit。
exit函数封装了系统调用_exit，exit函数还做了其他的事情。
# include <stdio.h>
# include <string.h>
# include <stdlib.h>
# include <unistd.h>
int main(void)
{
printf("i am testing"); //没有“\n”
sleep(2);
exit(EXIT_SUCCESS);
return 0;
}
代码运行的现象：休眠2秒后，在屏幕上打印“i am testing”.
因此，可以看出，exit函数会冲刷缓冲区……
现在换做_exit函数来终止进程。
# include <stdio.h>
# include <string.h>
# include <stdlib.h>
# include <unistd.h>
int main(void)
{
printf("i am testing"); //没有“\n”
sleep(2);
_exit(EXIT_SUCCESS);
return 0;
}
代码运行的现象：休眠两秒后，并没有在屏幕上显示预期的“i am testing”，就终止进程了。
因此可看出，_exit函数并不会冲刷缓冲区……
实际上，_exit系统调用函数只是简单地终止了进程，并不会做其他的工作。而exit函数在调用_exit函数之前还会做一些其他的工作：
- 执行用户定义的清理函数
- 冲刷缓冲区，关闭所有的流等。
- 调用_exit函数
main函数返回，本质上是把返回值作为参数传给exit函数，最后还是调用exit函数。
到此这篇关于C语言详解分析进程控制中进程终止的实现的文章就介绍到这了,更多相关C语言进程终止内容请搜索自由互联以前的文章或继续浏览下面的相关文章希望大家以后多多支持自由互联！