exec returning 255

I have my code running on the Mac and I am getting a 255 return code from exec. The following is the code:

    ret = execvp(pArgs[0], pArgs);  

    if (ret < 0) 
{
        ret = errno;
        exit(ret);
        return false;
   开发者_如何学编程 }
else if (processId < 0) 
{
    // fork() failed    
    return false;
    } 
else if(Wait)
{
    // forked successfuly so wait for exit
    if(waitpid(processId, &childstatus, 0) == processId)
    {
        // codesign command terminted, get return code
        if(WIFEXITED(childstatus))
        {
            if(pCmdRetStatus != NULL)
                *pCmdRetStatus = WEXITSTATUS(childstatus);
        }

    }   
}

Any thoughts on why the 255? Essentially an hdiutil call, a lot of times, I get 255.

UNIX (and therefore Mac OS X) exit statuses are forced into the range 0-255 unsigned.

So a return value of -1 from your call to execvp would be processed as -1 in your C code but would become 255 at the operating-system level due to the rules of the exit() function specification. Consider the following example:

bash> bash
bash2> exit -1
bash> echo $? # The exit status of the last command (bash2)
255

execvp returns an integer (-1) on error (and sets errno, which you should check/print (hint: perror)) which you pass to exit. Exit really only knows about EXIT_FAILURE and EXIT_SUCCESS, but it generally just passed on the value to the OS (which can usually handle 0-127 / 0-255, but don't count on it).

The only possible return values for exec are 0 and is -1. I'm guessing the type of the variable ret is wrong (unsigned char instead of int) and thus -1 is getting converted modulo 256 to 255.