echo $? returns jibberish when the return value of a cpp main func returns high numbers

Asked Mar 20 '18 at 21:06

Active Mar 20 '18 at 21:25

Viewed 43 times

I wrote the most basic main func:

int main()
{
 cout << "just to see it works";
 return 1234; 
}

afterwords I built the file and runned the file:

gcc <cpp fileName>.cc -lstdc++ -o main
./main

afterwords I ran:

echo $?

and my return value was 210 when I returned 999 instead of 1234 I got around 231 and when I returned numbers from around 0 to 250 I received the same number as aspected.

Why when returning high numbers I receive numbers around 210?

P.S. I was unable to find questions close enough to this one. Also, I didn't find in the manual of echo a good explanation of echo $? or a manual for echo $?

edited Mar 20 '18 at 21:25

asked Mar 20 '18 at 21:06

Tomer

2

Looks like you get numbers modulo 256. – HolyBlackCat Mar 20 '18 at 21:08
1

Convert the number to hexadecimal and take only the last 2 digits (aka mod 256). `1234 = 0x4d2`, `0xd2 = 210` . That seems to be what you are seeing – Justin Mar 20 '18 at 21:09
2

echo doesn't know about $?. That's done by the shell. – stark Mar 20 '18 at 21:10
Thanks! I think you are right that it is module 256. I wonder why it is like this but that already less relevant. – Tomer Mar 20 '18 at 21:14
Regarding the duplicate, I think it is not exactly a duplicate since the other question knows that echo $? gives modulo 256 and this question is for people who did notice this. – Tomer Mar 20 '18 at 21:18
1

Related: http://blogs.perl.org/users/mauke/2011/09/exit-statuses-and-how-works.html – melpomene Mar 20 '18 at 21:28
@melpomene perfect this really helps :-) – Tomer Mar 20 '18 at 21:38

echo $? returns jibberish when the return value of a cpp main func returns high numbers

0 Answers0