pclose返回值为什么要和256比较

include <errno.h>

include <stdio.h>

include <stdlib.h>

include <string.h>

include <unistd.h>

int main(int argc, char *argv[])
{
int status;
pid_t pid;

pid = fork();

if (0 == pid)
{
exit(atoi(argv[1]));
} else
{
wait(&status);
printf("status = %d\n", status);
if (WIFEXITED(status))
{
printf("WEXITSTATUS(status)=%d\n", WEXITSTATUS(status));
}
}

return 0;
}
该程序运行结果

pclose的返回值就是这里wait(&status)中status的值。