How to declare an empty char* and increase the size dynamically?

Question

Let's say I am trying to do the following (this is a sub problem of what I am trying to achieve):

int compareFirstWord(char* sentence, char* compareWord){
      char* temp; int i=-1;
      while(*(sentence+(++i))!=' ') { *(temp+i) = *(sentence+i); }
      return strcmp(temp, compareWord); }

When I ran compareFirstWord("Hi There", "Hi");, I got error at the copy line. It said I was using temp uninitialized. Then I used char* temp = new char[]; In this case the function returned 1 and not 0. When I debugged, I saw temp starting with some random characters of length 16 and strcmp fails because of this.

Is there a way to declare an empty char* and increase the size dynamically only to length and contents of what I need ? Any way to make the function work ? I don't want to use std::string.

Answer 1

In C, you may do:

int compareFirstWord(const char* sentence, const char* compareWord)
{
    while (*compareWord != '\0' && *sentence == *compareWord) {
        ++sentence;
        ++compareWord;
    }
    if (*compareWord == '\0' && (*sentence == '\0' || *sentence == ' ')) {
        return 0;
    }
    return *sentence < *compareWord ? -1 : 1;
}

With std::string, you just have:

int compareFirstWord(const std::string& sentence, const std::string& compareWord)
{
    return sentence.compare(0, sentence.find(" "), compareWord);
}