search for uses of int used instead of time_t

Question

I have a rather large c-code base, where every once in a while int is used instead of time_t. Any good ideas as to how to deal with this. Should I search the entire standard library for functions that either return time_t or take it as argument, or is there a smarter way?

As I understand it, time_t will be 64 bit on a 64-bit system, at least on my system, which is 64 bit. An int will only be 32 bit on a 64-bit system. Which means that such an int will run out in 2038 if used as time_t.

Answer 1

Assuming you're using gcc or clang, if you compile with the -Wconversion flag, it will warn you about converting from a larger type to a smaller type.

#include <stdio.h>
#include <time.h>

int main()
{
    time_t t = time(NULL);
    int i = t;

    printf("i=%d, t=%ld\n", i, t);

    return 0;
}

[dbush@db-centos7 ~]$ gcc -g -Wall -Wextra -Wconversion -o x1 x1.c
x1.c: In function ‘main’:
x1.c:7:5: warning: conversion to ‘int’ from ‘time_t’ may alter its value [-Wconversion]
     int i = t;
     ^

Answer 2

In the scenario you mention, (64-bit system, 32-bit integer) enabling compiler warnings, or use of a good static analysis program should highlight all the cases of implicit narrowing conversion of a 64-bit (time_t) integer to a 32-bit integer.

If you are using MISRA C:2012/2023, Rule 10.3 also applies...

So (for example):

time_t        nowTime1 = clock(); /* OK                            */
int           nowTime2 = clock(); /* Implicit narrowing to 32 bits */
unsigned int  nowTime3 = clock(); /* Implicit narrowing to 32 bits */
uint32_t      nowTime4 = clock(); /* Implicit narrowing to 32 bits */

However:

uint64_t      nowTime5 = clock(); /* Probably OK */
unsigned long nowTime6 = clock(); /* Probably OK */

See also time() and mktime(), as well as clock().

Assuming all your sources are the correct size, then any sinks (ctime(), difftime() etc) should be OK...