Question

Good evening,

I wrote the code below in C to read and print from a binary file a random hexadecimal string with a constant length, knowing a certain offset and the location of the string regarding the offset.

FILE *f = NULL;
unsigned char *buffer = NULL;
unsigned long fileLen;        
unsigned char bytes[] = {0x22, 0x22, 0x22, 0x22};

f = fopen(argv[1], "rb");
if (!f) 
{
    fprintf(stderr, "Unable to open %s\n", argv[1]);
    return -1;
}

fseek(f, 0, SEEK_END);
fileLen=ftell(f);
fseek(f, 0, SEEK_SET);

buffer=malloc(fileLen);
if (!buffer) 
{
    fprintf(stderr, "Memory error!\n");
    fclose(f);
    return -1;
}

fread(buffer, fileLen, 1, f);
fclose(f);

unsigned int *p = memmem(buffer, fileLen, bytes, 4);

if (!p) {

    return -1;
}

unsigned long off_to_string = 4 + 0x12 + ((void *)p) - ((void *)buffer);

for (unsigned long c = off_to_string; c < off_to_string+0x30; c++)
{
    printf("%.2X", (int)buffer[c]);
}

printf("\n");
free(buffer);

I would like to use this code in a Cocoa app, I tried to make something like:

NSMutableString *tehString = [[NSMutableString alloc] init];

for (unsigned long c = off_to_string; c < off_to_string+0x30; c++)
{
    [tehString appendString:...]
}

the problem is I must pass a NSString to appendString: and I don’t even know how to print its hexadecimal representation.

Thanks !

PS: Feel free to improve the code of the “hexadecimal string reader” 🙂

Answer 1

NSStrings can be created using the same string format specifiers.

so you could do this:

[tehString appendString:[NSString stringWithFormat:@"%.2X", (int)buffer[c]]];

caveat: I’ve just typed that in so it might be a little off – but you get the idea.