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In this noncompliant code example, if the given user input is 0, the division operation sends a SIGFPE signal to the program.
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#include<signal.h>
#include<stddef.h>
#include<stdlib.h>
volatile sig_atomic_t denom;
void sighandle(int s){
/* Fix the offending volatile */
if (denom == 0) {
denom = 1;
}
/* Everything is ok */
return;
}
int main(int argc, char *argv[]){
int result = 0;
if (argc < 2) {
return 0;
}
denom = (int)strtol(argv[1], (char **)NULL, 10);
signal(SIGFPE,(*sighandle));
result = 100/denom;
return 0;
}
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In the compliant solution, the only portably safe way to leave a SIGFPE, SIGILL, or SIGSEGV handler is through abort() or /_Exit(). In the case of SIGFPE, the default handler calls abort(), so no user-defined handler is actually needed. The handler shown is only for consistency.
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#include<signal.h>
#include<stddef.h>
#include<stdlib.h>
volatile sig_atomic_t denom;
void sighandle(int s){
/* No recovery */
abort();
}
int main(int argc, char *argv[]){
int result = 0;
if (argc < 2) {
return 0;
}
denom = (int)strtol(argv[1], (char **)NULL, 10);
signal(SIGFPE,(*sighandle));
result = 100/denom;
return 0;
}
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