Tire Code

tire.c

#include <regex.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>

/**
 * Convert a regex match into an integer
 */
int to_integer(regmatch_t match, const char* str) {
    const char *end = &str[match.rm_eo];
    return strtol(&str[match.rm_so], (char**)&end , 10);
}

struct tire {
    double width;
    double ratio;
    double rim;
};

bool parse_tire_code(char * code, struct tire *par)
{
    // Build regular expressions
    regex_t regex;
    const char *re = "^(P|LT|ST|T)([0-9]{3})/([0-9]{2,3})[BDR ]([0-9]{2})$";
    if (regcomp(&regex, re, REG_EXTENDED) != 0) {
        fprintf(stderr, "Could not compile regex\n");
        abort();
    }

    // Execute regular expression
    const int groups = 5;
    regmatch_t matches[groups];
    if (regexec(&regex, code, groups, matches, 0))
        return 1;

    // Extract components
    const char * codi = "P225/55R15";
    double width = to_integer(matches[2], codi) / 1000.0; // mm to meters
    double ratio = to_integer(matches[3], codi) / 100.0; // percent to ratio
    double rim = to_integer(matches[4], codi) * 25.4e-3; // inches to meters

    // Check for errors
    if (width == 0 || ratio == 0 || rim == 0 || ratio > 200) {
        return 1;
    }

    // Atomic return
    par->width = width;
    par->ratio = ratio;
    par->rim = rim;

    regfree(&regex);
    return 0;
}

int main()
{
    struct tire par;
    if (parse_tire_code("P225/55R15", &par)) {
        exit(1);
    }
    printf("%f %f %f\n", par.width, par.ratio, par.rim);
}