// Andrew Taylor - andrewt@unsw.edu.au // 08/06/2020 // Convert a hexadecimal string to an integer /*``` \$ dcc hex_string_to_int.c -o hex_string_to_int \$ dcc hex_string_to_int.c -o hex_string_to_int \$ ./hex_string_to_int 2A 2A hexadecimal is 42 base 10 \$ ./hex_string_to_int FFFF FFFF hexadecimal is 65535 base 10 \$ ./hex_string_to_int DEADBEEF DEADBEEF hexadecimal is 3735928559 base 10 \$ ```*/ #include #include #include uint32_t hex_string_to_int(char *hex_string); int hex_digit_to_int(int ascii_digit); int main(int argc, char *argv[]) { if (argc != 2) { fprintf(stderr, "Usage: %s \n", argv[0]); return 1; } char *hex_string = argv[1]; uint32_t u = hex_string_to_int(hex_string); printf("%s hexadecimal is %u base 10\n", hex_string, u); return 0; } uint32_t hex_string_to_int(char *hex_string) { uint32_t value = 0; for (int which_digit = 0; hex_string[which_digit] != 0; which_digit++) { int ascii_hex_digit = hex_string[which_digit]; int digit_as_int = hex_digit_to_int(ascii_hex_digit); value = value << 4; value = value | digit_as_int; } return value; } // given the ascii value of a hexadecimal digit // return the corresponding integer int hex_digit_to_int(int ascii_digit) { if (ascii_digit >= '0' && ascii_digit <= '9') { // the ASCII characters '0' .. '9' are contiguous // in other words they have consecutive values // so subtract the ASCII value for '0' yields the corresponding integer return ascii_digit - '0'; } if (ascii_digit >= 'A' && ascii_digit <= 'F') { // for characters 'A' .. 'F' obtain the // corresponding integer for a hexadecimal digit return 10 + (ascii_digit - 'A'); } fprintf(stderr, "Bad digit '%c'\n", ascii_digit); exit(1); }