ft_strrchr

Subject

STRRCHR(3) (simplified)

NAME
    strrchr -- locate character in string
SYNOPSIS
    char *strrchr(const char *s, int c);
DESCRIPTION
    The strrchr() function is identical to strchr(), except it locates the last occurence of c.
RETURN VALUES
    The function strrchr() returns a pointer to the located character, or NULL if the character does not appear in the string.

Understandable explanation

This function is fairly easy to understand, it does the same thing as strchr(), but locates the last occurence of c.

Hints

ft_strrchr.c

char *ft_strrchr(const char *s, int c)
{
    /* we can use basically the same code as ft_strchr() but not returning
     * the value as soon as we find the character, just setting a variable
     * each time, and returning it at the end of the function
     */
    /* loop over the whole string */
    /* check if current character is equal to the one we have to find */
    /* once we looped over the whole string, check again for the character
     * in case the character we have to find is '\0'
     */
    /* if we didn't find c in the string, return NULL */
}

Commented solution

ft_strrchr

ft_strrchr.c

#include "libft.h"

char *ft_strrchr(const char *s, int c)
{
    unsigned int i;
    char *res;
    char cc;
    
    /* we convert c to a char as we got it as an int */
    cc = (char) c;
    /* we set res as NULL at the beginning so if we don't find 
     * any occurence of c, the function will return NULL
     */
    res = NULL;
    i = 0;
    /* looping over the whole string s */
    while (s[i])
    {
         /* if the current character is equal to cc 
         * this means we found an occurence of cc in the string
         * therefore, we set res as the address of the character
         */
        if (s[i] == cc)
            res = (char *) &s[i];
        /* we then advance in the string to search for another
         * occurence of cc
         */
        i++;
    }
    /* once we looped over the whole string, if we didn't find an
     * occurence of cc, we have to check if cc is equal to '\0'
     * so we check once again if the current character is equal to cc
     * if this is the case, we set res as the address of the '\0' char
     */
    if (s[i] == c)
        res = (char *) &s[i];
    /* when we reach the end of the function, we return res
     * since we looped over the whole string and set res as the address
     * of the last occurence of c we found, this will return a pointer 
     * to the last occurence of c
     * and if we didn't find any occurence of c, since res was set to 
     * NULL at the very beginning of the function, the function will
     * return NULL
     */
    return (res);
}