C: set bits in long integer

Tillotson

Like the title says I'm trying to read and set bits in a long integer, here's my code:

 23 typedef long type_t;
 24 //typedef int type_t;
 25 
 26 int main() {
 27         type_t x = 3;
 28         for (type_t i = 0; i < sizeof(type_t) * 8; i++) {
 29                 if (x & (1 << i)) printf("T");
 30                 else printf(".");
 31         }
 32         printf("\n");
 33 }

long: "TT..............................TT.............................."
int: "TT.............................."

Why do I get the repeating pattern when reading the long integer?

Sparks

Possibly because the 1 in line 29:

if (x & (1 << i)) printf("T");

isn't a long int, but an int (C won't declare it a long int unless it has to or you tell it to). Try this and see if it fixes it:

if (x & (1L << i)) printf("T");

But that won't work for int then.
Perhaps if you had

type_t foo = 1;

And later used

if (x & (foo << i)) printf("T");

That might be the better way.


edit: just tested it and it looks like that was it:

#include <stdio.h>

typedef long type_t;
//typedef int type_t;
int main()
{
    type_t x = 3;
    type_t foo = 1;
    for (type_t i = 0; i < sizeof(type_t) * 8; i++) {
        if (x & (foo << i)) printf("T");
        else printf(".");
    }
    printf("\n");
}

You do know that that will only compile in a GNU99/C99 compiler or later, right?

Tillotson

Thank you!!

I spent an embarrassing amount of time flailing around not seeing the source of the problem.

Sparks

It's just fresh eyes.
If it makes you feel any better, I lost two hours this week because I didn't notice I had an 'i' instead of a 'j' in an array index inside a loop; in the Monaco console font, the two are annoyingly similar. Got up, walked away, had coffee, came back, sprayed coffee all over screen when I spotted it sitting there, laughing at me...

FruitLover

Sparks wrote: »

I lost two hours this week because I didn't notice I had an 'i' instead of a 'j' in an array index inside a loop

Made a similar mistake myself many moons ago using 'i' and 'j' as outer and inner loop counters. Since then, I've systematically used 'ctr', 'ctr_outer' and 'ctr_inner' for loop counters...