CODEWITHSUNDEEP
cfgets
Setekorrales
Setekorrales

Reputation: 105

using fgets() to extract lines from a file not working

I'm trying to develop a function that reads each line of a text file and the it stores them in an array of strings (char**) but fgets() doesnt seem to work, it always return a null character.

Here is the function

 char** getLines(FILE* fp){

    char** lines;
    int numberOfLines; //number of lines int the file
    char ch; //aux var
    int i; //counter

    while(!feof(fp)){
        ch = fgetc(fp);
        if( ch == '\n'){
            numberOfLines++;
        }
    }

    lines = malloc(numberOfLines*sizeof(char*));

    if (lines==NULL){
        fprintf(stderr,"Error, malloc failed");
        exit(1);
    }

    for(i = 0; i<numberOfLines; i++){
        lines[i] = malloc(MAX_LENGTH*sizeof(char)); //MAX_LENGTH = 128
    }

    i=0;
    while(fgets(lines[i], MAX_LENGTH,fp)){
        printf("Line %d: %s \n",i,lines[i]);
        i++;
    }

    return lines;

}

The function never gets inside the while loop so it doesn't print anything I'm also using a very simple input file:

test line 1
test line 2
test line 3
test line 4

Hope you can help me, Thank you in advance.

Upvotes: 2

Views: 1693

Answers (1)

Raynigon
Raynigon

Reputation: 701

You are already on the end of the file before entering the while loop.

Take a look here http://en.cppreference.com/w/cpp/io/c/rewind

Moves the file position indicator to the beginning of the given file stream. The function is equivalent to std::fseek(stream, 0, SEEK_SET); except that end-of-file and error indicators are cleared. The function drops any effects from previous calls to ungetc.

Check if this works:

char** getLines(FILE* fp){
    /* ...... */
    i=0;
    rewind(fp); // Rewind here
    while(fgets(lines[i], MAX_LENGTH,fp)){
        printf("Line %d: %s \n", i, lines[i]); // Also use the index as first parameter
        i++;
    }

    return lines;

}

Upvotes: 3

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