FB interview

string_serialization.c

/**
 * @file string_serialization.c
 * compile, gcc -std=c99 string_serialization.c ...
 *
 * @author Frank Dai
 * @email soulmachine@gmail
 */
#include <stdio.h>
#include <stdlib.h>  /* for strtoll, ato */
#include <string.h>
#include <limits.h>
#include <assert.h>

typedef long long int64_t;

#define SEPARATOR '#'

/* length of 64-bit signed integer, i.e 9223372036854775807LL */
#define MAX_LEN  19
#define RADIX   10

/**
 * convert int to string.
 * @param[in] n number
 * @param[out] s string
 * @return the number of characters
 */
static int int_to_str(int64_t n, char s[MAX_LEN+1]) {
    snprintf(s, MAX_LEN+1, "%lld", n);
}

/**
 * convert string to int.
 * @param[in] s a string begins with numbers
 * @param[out] n address of an int
 * @return the numbers of characters
 */
static int str_to_int(const char *s, int64_t *n) {
    char *end;
    *n = strtoll(s, &end, 10);
    return end - s;
}

/**
 * string format: "len1#str1str2", length befor separator character #,
 * is the length of first string
 */

/**
 * @brief concat
 * @param[in] s1 the first string, primitive string
 * @param[in] s2 another string, primitive string
 * @param[out] s structured string
 * @return a new allocated buffer which contains the concated string
 */
char* string_concat(const char *s1, const char *s2) {
    char *result; /* the concated string */
    int len1, len2; /* length of s1, s2 */
    char len1_str[MAX_LEN + 1];
    int len1_len; /* length of len_str */

    if (s1 == NULL)
        len1 = 0;
    else
        len1 = strlen(s1);

    if (s2 == NULL)
        len2 = 0;
    else
        len2 = strlen(s2);

    len1_len = int_to_str(len1, len1_str);
    result = (char*) calloc(len1_len + 1 + len1 + len2 + 1, sizeof(char));

    strncpy(result, len1_str, len1_len);
    result[len1_len] = SEPARATOR;
    if (len1 > 0) {
        strncpy(result + len1_len + 1, s1, len1);
    }
    if (len2 > 0) {
        strncpy(result + len1_len + 1 + len1, s2, len2);
    }

    return result;
}

/**
 * @brief split
 * @param[in] s received string from remote machine, structured string
 * @param[out] s1 the first string, primitive string
 * @param[out] s2 another string, primitive string
 * @return 0 if success, otherwise error code
 */
int string_split(const char *s, char **s1, char **s2) {
    int len1, len2;
    int len1_len; /* digits of len1 */
    const int len = strlen(s);

    if (len < 2) { /* malfunctioned string */
        *s1 = NULL;
        *s2 = NULL;
        return -1;
    }
    len1_len = str_to_int(s, &len1);
    len2 = strlen(s + len1_len + 1);

    *s1 = (char*) calloc(len1 + 1, sizeof(char));
    *s2 = (char*) calloc(len2 + 1, sizeof(char));
    strncpy(*s1, s + len1_len + 1, len1);
    strncpy(*s2, s + len1_len + 1 + len1, len2);

    return 0;
}

void unit_tests() {
    char s[MAX_LEN + 1];
    int n;

    int_to_str(LONG_LONG_MIN, s);
    printf("%s\n", s);
    str_to_int(s, &n);
    printf("%lld\n", n);

    int_to_str(LONG_LONG_MAX, s);
    str_to_int(s, &n);
    printf("%lld\n", n);

    int_to_str(0, s);
    str_to_int(s, &n);
    printf("%lld\n", n);

    str_to_int("0#abc", &n);
    printf("%lld\n", n);
    str_to_int("9223372036854775807#abc", &n);
    printf("%lld\n", n);
}

void unit_tests1() {
    char *s, *s1, *s2;

    s = string_concat("a", "b");
    string_split(s, &s1, &s2);
    printf("%s %s %s\n", s, s1, s2);
    free(s1);
    free(s2);
    free(s);

    s = string_concat(NULL, "b");
    string_split(s, &s1, &s2);
    printf("%s %s %s\n", s, s1, s2);
    free(s1);
    free(s2);
    free(s);

    s = string_concat("", "b");
    string_split(s, &s1, &s2);
    printf("%s %s %s\n", s, s1, s2);
    free(s1);
    free(s2);
    free(s);

    s = string_concat("a", "");
    string_split(s, &s1, &s2);
    printf("%s %s %s\n", s, s1, s2);
    free(s1);
    free(s2);
    free(s);

    s = string_concat("a", NULL);
    string_split(s, &s1, &s2);
    printf("%s %s %s\n", s, s1, s2);
    free(s1);
    free(s2);
    free(s);

    s = string_concat(NULL, NULL);
    string_split(s, &s1, &s2);
    printf("%s %s %s\n", s, s1, s2);
    free(s1);
    free(s2);
    free(s);

    s = string_concat("", "");
    string_split(s, &s1, &s2);
    printf("%s %s %s\n", s, s1, s2);
    free(s1);
    free(s2);
    free(s);
}

int main(void) {
    //unit_tests();
    unit_tests1();
    return 0;
}