Exit code from Exit (-1) or return ( -1) shell Why is the 255_linux shell

Now I've written a Hello World program to take a look at it:

Filename:main.c
 #include <stdio.h>
 int main (void)
 {
   printf ("Hello wolrd!\n");
   return (-);  
 }

Compile execution: gcc main.c &&/a.out

Now let's take a look at the return value of the previous execution in the current shell, is "-1"?

inuyasha@inuyasha-aspire-4741:~/Desktop $ gcc main.c &&/a.out

Hello world!

inuyasha@inuyasha-aspire-4741:~/Desktop $ echo $?

255

Ah, the result why "255"? Call a program, program exit-1, get results not "-1"?

The following references from: http://www.laruence.com/2012/02/01/2503.html

The problem is simply that the return in exit or main function can only use the value between 0~255. -The unsigned value of 1 is 255.

What about the complicated point?

We know that in a shell, a command, a program, is executed by a fork (then exec), and the exit code of the program is collected by the shell (the parent process) and then reported to us.

pid_twait (int *statloc);

And for wait, historically, he will return a 16bit interge via Statloc (now also 32-bit, but compatible with existing designs). In this 16bits interge, the high 8 bits are the value of the program exit (exit, or return), while the low eight digits indicate the signal that caused the program to exit (one of them indicates whether a core file is produced), and if the program is normal exit, then the lower eight bits are 0[1].

So, if we return 1, and because we are exiting normally, the child process that the shell collects through wait is:

11111111 00000000

And the high eight-bit as a unsigned, is 255.

In addition, to add, in the Linux built-in shell commands, many will adhere to an exit status code agreement, the specific value of the corresponding meaning [2]:

number

Exit Code	meaning	Example	Comments
1	Catchall for general errors	Let "var1 = 1/0″	Miscellaneous errors, such as "divide by zero" and other impermissible operations
2	Misuse of Shell Builtins (according to Bash documentation)	Empty_function () {}	Seldom seen, usually defaults to exit code 1
126	Command invoked cannot execute		Permission problem or command is not a executable
127	"Command not Found"	Illegal_command	Possible problem with $PATH or a typo
128	Invalid argument to exit	Exit 3.14159	Exit takes only-integer args in the range 0–255 (I/footnote)
128+n	Fatal error Signal "n"	kill-9 $PPID of script	$? returns 137 (128 + 9)
130	Script terminated by Control-c		CONTROL-C is fatal error signal 2, (130 = 128 + 2, and so on above)
255*	Exit Status out of range	Exit-1	Exit takes only-integer args in the range 0–255