print uint32_t to string in C but not it's literally value

Question

I'm reading an image file and I want to show the format it was compressed in console.

In example, I read this: format = 861165636 (0x33545844), as my CPU reads and writes in Little Endian I do format = __builtin_bswap32(format); so now format = 1146639411 (0x44585433), and 0x44585433 = "DXT3" in ASCII.

I want to print this ("DXT3") but not using and extra variable, I mean, something like this printf("Format: %s\n", format); (that obviously crash). There's a way to do it?

So you want to interpret a uint32_t buffer as if it were a four byte array of ASCII characters? — jwdonahue, Jan 18 '21 at 23:00
@jwdonahue you literally summarized all the question in 1 sentence :P — TheCatcherInTheCPP, Jan 18 '21 at 23:03

0___________ · Accepted Answer · 2021-01-18T23:33:31.750

1

order paratameter indicates if you want to start from the most significant byte or not.

void printAsChars(uint32_t val, int order)
{   
    if(!order)
    {
        putchar((val >> 0) & 0xff);
        putchar((val >> 8) & 0xff);
        putchar((val >> 16) & 0xff);
        putchar((val >> 24) & 0xff);
    }
    else
    {
        putchar((val >> 24) & 0xff);
        putchar((val >> 16) & 0xff);
        putchar((val >> 8) & 0xff);
        putchar((val >> 0) & 0xff);
    }
}

int main(int argc, char* argv[])
{
    printAsChars(0x44585433,0); putchar('\n');
    printAsChars(0x44585433,1); putchar('\n');
}

https://godbolt.org/z/WWE9Yr

Another option

int main(int argc, char* argv[])
{
    uint32_t val = 0x44585433;
    printf("%.4s", (char *)&val);
}

https://godbolt.org/z/eEj755

edited Jan 18 '21 at 23:33

answered Jan 18 '21 at 23:22

0___________

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Perhaps you could explain why the order parameter is needed? The OP probably hasn't considered little/big endianess. – jwdonahue Jan 18 '21 at 23:25
I loved the simplicity of the second option, and thanks for that website too, It goes directly to my bookmarks. – TheCatcherInTheCPP Jan 18 '21 at 23:45

score -3 · Answer 2 · answered Jan 18 '21 at 23:02

-3

printf("Format: %c%c%c%c\n", format << 24, format << 16, format << 8, format & 256); or something like that. untested. Maybe you need to mask the chars.

answered Jan 18 '21 at 23:02

rurban

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Your code will not work. It is a good habit **to test the code before** answering the question. If you do not test - simply do not answer – 0___________ Jan 18 '21 at 23:28

print uint32_t to string in C but not it's literally value

2 Answers2