Populating Heap (malloc) with a string array

Question

hello, i'm trying to populate the heap with a string array, but the console gave me nothing when i compiled. I don't know what I did wrong...

void spellCheck(char article[], char dictionary[]) {
    int i = 0;
    char* tempArticle;
    while ( article[i] != '\0'){
     i++;
    }
    tempArticle = malloc(i);
    i=0;
    while (article[i] != '\0'){
     strcpy(tempArticle, article[i]);
    }
    printf("%s", tempArticle);
}

Answer 1

You can use strlen for the string length. Also, you are using strcpy a lot of times. Ultimately, you are copying only the null terminator. The function strcpy does this work for you. strcpy copies each character up to an expected null terminator into your new buffer. In other words, you don't use it to copy a character at a time but a string at a time. Although, I'm not sure what your function is intended to do at this point.

void spellCheck(char article[], char dictionary[]) {
    int i = 0;
    char* tempArticle;

    /*while ( article[i] != '\0'){
     i++;
     }*/

    tempArticle = malloc((strlen(article)+1) * sizeof(char));
    /*i=0;
    while (article[i] != '\0'){
     strcpy(tempArticle, article[i]);
    }*/

     strcpy(tempArticle, article);
    printf("%s", tempArticle);
}

Again, in other words, your second loop was essentially trying to copy a smaller and smaller string into the tempArticle buffer until you ended up copying an empty string into it.

(minor point, another answerer pointed out that your second loop was an infinite loop because i was not being incremented. However, you still the had the other problems mentioned)

Edit

So to answer the comment of converting it to lowercase. In general to convert an entire string to lowercase, you would just do something like this:

char s[] = "THE String.";
char *c;
for(c = s; *c != '\0'; c++)
    *c = (char)tolower(*c);

Answer 2

strcpy copies an entire string, not simply a character. http://cplusplus.com/reference/clibrary/cstring/strcpy/

Also, strlen() returns the length of a string. You could make your code much shorter and readable by having it be something like this:

void spellCheck(char article[], char dictionary[])
{
    char *tempArticle = malloc(sizeof(char)*(strlen(article)+1));
    strcpy(tempArticle, article);
    // deal with tempArticle
    free(tempArticle)
}

the +1 in the malloc line is so that the end-of-line character gets a space.

Answer 3

This

i=0;
while (article[i] != '\0') {
  strcpy(tempArticle, article[i]);
}

is an infinite cycle (unless article[0] happens to be 0). You need to fix that for sure. Although there are quite a few things that need to be fixed in that code, but this is a good start.

Answer 4

Hello, you are not increasing i on:

while (article[i] != '\0'){ strcpy(tempArticle, article[i]); }

Answer 5

The problem is in here:

i = 0;
while (article[i] != '\0') {
  strcpy(tempArticle, article[i]);
}

Strcpy copies a whole string, and you forgot to increment i, and the strcpy expect the second argument to be a char pointer (not a char). So you are copying garbage into tempArticle over and over again.

Try this:

for (int i=0; article[i] != '\0'; ++i) {
  tempArticle[i] = article[i];
}

There are other design issues in your code, but this is probably the only one preventing things from working.

Answer 6

A lot of people seem to think you're trying to copy a single string. The subject and your intro doesn't seem like that's the case. Are you sure you're not trying to do something like this?

void spellCheck(char *article[], char dictionary[]) {
    int i = 0;
    char** tempArticle;
    while (article[i] != NULL) {
        i++;
    }
    tempArticle = malloc(i*sizeof(char*));
    i=0;
    while (article[i] != NULL) {
        tempArticle[i] = strdup(article[i]);
        i++;
    }
}