converting string to hex

Question

I have a string that has 0111111100000000000000000000101

I wanted to convert this to hex, so I used the code below

    int assembledHex;
    sscanf(buffer, "%x", &assembledHex);
    printf("this is the assembled hex %x\n",assembledHex);

but when I print it, it gives me 101. I thought sscanf can convert to hex from a string, what am I doing wrong and how can I fix it. The result I want is 0x3F800005

Answer 1

This is not checked or anything, and also quite slow, but it's a quick start:

unsigned int bin_to_int(const char *s) {
    int i;
    unsigned int result;

    result = 0;

    if (s[0] == '1') result++;

    for (i = 1; i < strlen(s); i++) {
        result <<= 1;

        if (s[i] == '1') {
            result++;
        }
    }

    return result;
}

Answer 2

Your sscanf is reading the string as HEX, but the string is written in binary. You get "101" because int can only store the first 8 digits - each digit is 4 bits, so two digits=8 bits=1 byte, and 8 digits are 4 bytes, which is the size of int . So you actually store "00000101", buy printf does not print the leading zeroes so you get "101".