Find hex values inside a string in C?

Question

I have a long string "given_string", and I'm trying to find hex values within that string. Here's a simplified example:

/* Find a sub-string in a given string: */
    char * given_string = "This is a long given string. 0xff. Happy Programming! ";
    
    int length = strlen(given_string);
    for (int i = 0; i < length; i++)
    {
        if(given_string[i] == 0xff)
        {
            printf("%c\n", given_string[i]);
        }
    }

Though when I run the above code, I get this error:

warning: comparison of constant 255 with expression of type 'char' is always false
      [-Wtautological-constant-out-of-range-compare]
        if(given_string[i] == 0xff)

           ~~~~~~~~~~~~~~~ ^  ~~~~
1 warning generated.

How do I find hex values in a string?

Answer 1

Perhaps you've overlooked something. All the characters in the string are actually stored as ASCII values. Since ASCII values run from 0 to 127, the code will never find 255.

Maybe you should be looking for the ASCII values representing the hex values you are seeking?

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