The return code of an application is an int16_t?

Question

When talking about starting a new process, you can do it using int system(char* command). If you pass an non NULL parameter, you can get:

• -1 if the child process cannot be started;
• a return code of the child process otherwise;

note: in Unix/Linux the return code is located on the higher eight bits of the result, while the lower eight bits contain the termination reason code>{1}<, so a retcode equal to 1 will be returned as 256; you can get the actual return code by shifting the value eight bits to the right; there is also a macro named WEXITSTATUS() that does it for you.

Searching for the implementation of WEXITSTATUS() it's a shift 8 bits to the right.

#define WEXITSTATUS(x) (_W_INT(x) >> 8)

This is the reason why I tend to think that return codes are 2 bytes (and also from >{1}<). The quote is from a C course found online.

P.s I would like to know the difference between the return code and termination reason code, aren't they the same?

Answer 1

There s different reasons for termination:

• process terminates calling return (explicitly or not)
• process terminates after signal delivery
• process stopped after signal delivery. This one is not really termination but need to be caught in many situations.

For each of theses terminations a code is accessible, respectively:

• value returned (only low eight bits of it)
• signal number
• signal number