I am on ubuntu linux 10.04 I have the following
#simplec.c
#include "stdio.h"
int main()
{
printf("Hello World\n");
system("ps -H");
return 开发者_如何学Go12;
}
AND
#callsimplec.c
#include "stdio.h"
int main()
{
int ret =0;
ret = system("./simplec");
printf("In callsimplec ret is %d\n", ret);
}
When I do
gcc callsimplec.c -o callsimplec
gcc simplec.c -o simplec
./callsimplec
I get:
Hello World
PID TTY TIME CMD
27238 pts/2 00:00:00 bash
28066 pts/2 00:00:00 callsimplec
28067 pts/2 00:00:00 simplec
28068 pts/2 00:00:00 ps
In callsimplec ret is 3072
So I figured out that 3072 is printed because 256 times 12 is 3072. Whatever return value I use in simplec.c I get that value multiplied by 256 as the output in print. Why is that? I am just trying to make sense of it.
The value returned by system
should be used with the macros: WEXITED, WIFEXITSTATUS etc.
The value returned by system
(and by the wait
family) is, acording to case:
Normal termination:
15 ............. 8 ............. 0 exit status 0x00
Killed by signal:
15 ............. 8 7............ 0 unused killer signal
Stopped by signal
15 ............. 8 ............. 0 stop signal 0x7f
Continued by signal
15 ............................. 0 0xFFF
So in your case the process exited normally and system returned 12
shifted 8 times.
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