exit(-1)或者return(-1)shell得到的退出码为什么是255

下面我写了一个hello world程序，一起看看吧：

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

编译执行：gcc main.c && ./a.out

现在我们看看在当前shell中返回上一个执行过程的返回值是多少，是 “-1” 吗？

inuyasha@inuyasha-Aspire-4741:~/桌面$ gcc main.c && ./a.out

hello world!

inuyasha@inuyasha-Aspire-4741:~/桌面$ echo $"255"呢？调用一个程序, 程序退出-1, 得到结果不是“-1”吗？

以下引用自：http://www.laruence.com/2012/02/01/2503.html

这个问题简单的说, 是因为exit或者main函数中的return, 只能使用0~255之间的值. -1 的unsigned值就是255.

那么复杂点的说呢"border-bottom: silver 1px solid; border-left: silver 1px solid; padding-bottom: 0px; text-transform: none; background-color: rgb(255,255,255); text-indent: 0px; margin: 0px; padding-left: 0px; letter-spacing: normal; padding-right: 0px; border-collapse: collapse; font: 13px/23px Verdana, Arial, Helvetica, sans-serif; white-space: normal; color: rgb(17,17,17); border-top: silver 1px solid; border-right: silver 1px solid; word-spacing: 0px; padding-top: 0px; -webkit-text-stroke-width: 0px"> Exit Code Number 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 an 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 (see first footnote) 128+n Fatal error signal ”n” kill -9 $PPID of script $"Apple-converted-space"> returns 137 (128 + 9) 130 Script terminated by Control-C   Control-C is fatal error signal 2, (130 = 128 + 2, see above) 255* Exit status out of range exit -1 exit takes only integer args in the range 0 – 255