在字符串中查找按字典顺序排列的最大单词 - C 指针

Question

EDIT: Edited everything sorry for misunderstandings.

I'm trying to write a function to find the lexicographically greatest word in a string.

A word is defined as so: contains a letter - can use isalpha() - and does not contain spaces - can use isspace()

If s = "He llo wor ld "

s contains the following words: He, llo, wor, l, d.

To find the lexicographically greatest word between two strings, I can use strcmp.

The function prototype is: char *biggestWord(char *s) and it should return the lexicographically greatest word.

I'm literally stuck with it for hours. Here's what I tried to do:

I'm stuck on what to do next. My algorithm idea wouldn't even work if there is two spaces in a row.

char *biggestWord(char *s) {
//We will find the first string and compare it to each one of the new strings
//We will keep the value of the higher string everytime
char *res;
char *temp;
int indexStart = 0; //Will contain the index of the first character to then store on temp
int indexEnd = 0; //Will contain the index of the last character to then store on temp
for(int i = 0; s[i] != '\0'; i++) {
    if(isspace(s[i])) {
        indexEnd = i - 1;
        temp = myStrCpy(s, indexStart, indexEnd); //Will extract the string using start and end index, and put it into temp
        indexStart = i+1;
    }
}

}

Answer 1

Here is a possible solution:

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <ctype.h>

char* biggestWord(char* s) 
{
    // Create a buffer for bigest word
    char* buf = calloc(strlen(s) + 1, sizeof(char));
    if (buf == NULL)
        return NULL;
    // Create a buffer for current word
    char* word = malloc(strlen(s) + 1 * sizeof(char));
    if (word == NULL)
        return NULL;

    int j = 0;
    for (int i = 0; s[i]; i++) {
        if (isspace(s[i])) {
            // We found end of word, replace the space by a nul byte
            strncpy(word, s + j, i - j);
            word[i - j] = 0; // nul terminate
            if (strcmp(buf, word) < 0) {
                // we got a bigger word according to strcmp()
                strcpy(buf, word);
                // skip remaining spaces
                while (s[i] && isspace(s[i]))
                    i++;
                // Remember where a word starts
                j = i;
            }
        }
    }
    free(word);
    return buf;   // cAller must call free()
}

void main(void)
{
    char* res = biggestWord("He llo wor l d ");
    if (res) {
        printf("Result=\"%s\"", res);
        free(res);
    }
}

biggestWord return a pointer to dynamically allocated string, so it must be freed by caller.