Question

Hello I have a function which populates a 2D array, consisting of words. I want to simply return the value of the pointer I entered the function with, but for some reason the pointer is now pointing to something else, strangely. I want to know how to fix this. Also wouldn't it be possible to do pointer arithmetic to fix this issue?(That's not what I want to do, I want to see what the issue is and fix it that way, but it'd be nice to know anyway). So it's supposed to be a 500 x 5 array, and even though I assign strings to 'dictPointer[i]', which I thought is supposed to represent "*dictPointer" and not "dictPointer", it seems as though I shouldn't have an issue. I need it to be this way because I wanted to print words starting from the initial pointer value. Also note that dictPointer is a pointer to pointer( **dictPointer)

char** readAndPopulateArray(FILE *f, char *fileName, char **dictPointer, int x ) { // x represents the number of words 
    // point is the word pointer
    int i = 0;
    char tempStr[80];
    char ch;
    f = fopen(fileName, "r");
    if ( f == NULL ) {
        printf("Cannot open %s. Verify it's in the right location\n", fileName);
    }

    while (fscanf(f, "%s", tempStr) == 1 ) {
        if( strlen(tempStr) == 4 ) {
            if(i == 0 ) {
                printf("Entering dictpointer points to %p\n", *dictPointer);
            }
            dictPointer[i] = tempStr;
                        if ( i == 499 ) {
                printf("Exiting dictPointer points to %p\n", *dictPointer);
            }
        }
        i++;
    }

    return dictPointer;
}

Below was how I called malloc for the matrix:

char** makeStringWordArray(int x, int letters ) { // x represents number of words, function stores one character each per word
    // letters represents number of letters in each word
    char *hold;
    int i, j = 0;
    char **dict = (char **)(malloc(x * sizeof(char*)) );
    for (i = 0; i<x; i++ ) {
            dict[i] = (char*)(malloc(letters*sizeof(char) + 1 ) );
        }

    return dict;
}

Answer 1

You assign every dictPointer[i] to the same pointer tempStr. Then the lifetime of tempStr ends at the end of readAndPopulateArray, making dictPointer[i] invalid.

Perhaps you meant

strcpy(dictPointer[i], tempStr);

Double Pointer being modified in an array mysteriously

1 个答案: