Reading File

I am trying to read a file and store each line in an array, but I am having a bit of trouble doing it.

This is my attempt, I know there must be a much simpler way to do this but after a few hours searching google, I could't figure out how to use malloc on 2D arrays.

When I run the code I only get the last line of the text file printing out, not all if like I am trying to do.

Code:

---

typedef struct{
    char text[50];
} line;

line *textfile;
FILE *f;

int main(int argc, char *argv[]){
    f = fopen(argv[1],"r");
    textfile = malloc(sizeof(line));
    fgets(textfile[0].text,50,f);
    int numlines = 1;
    while(!feof(f)){
        textfile = malloc(sizeof(line)*(numlines+1));
        fgets(textfile[numlines].text,50,f);
        numlines++;
    }
    int n = 0;
    while(n<numlines){
        printf("%s",textfile[n].text);
        n++;
    }

    return 0;
}

---

> textfile = malloc(sizeof(line)*(numlines+1));
You keep losing all the lines you´ve copied so far.
Look into using realloc instead.

> while(!feof(f))
There is a FAQ on why this is bad.

Okay, so my code now looks like

Code:

---

typedef struct{
        char text[50];
} line;


int main(int argc, char *argv[]){
        f = fopen(argv[1],"r");
        textfile = malloc(sizeof(line));
        fgets(textfile[0].text,50,f);
        int numlines = 1;
        textfile = realloc(textfile,2*sizeof(line));
        while(fgets(textfile[numlines].text,50,f) != NULL){
                textfile = realloc(textfile,2*sizeof(line));
                numlines++;
        }

---

The way I understand realloc is that the second argument was how much additional space is to be added, but when try to add sizeof(line) it just crashed so I changed it to 2*sizeof(line)

But when I compile and run the code, it doesn't store the third line in the text file. Every other line is done fine.

realloc() doesn't ask for how much space is to be added. It wants the total amount of space to be allocated. So you will have to keep a running "size of buffer" count and add to that before calling realloc().

Code:

---

int BuffSize = 0;

// in your loop
BuffSize += (strlen(NewLine) +1);
realloc (Buffer, Buffsize);

---

The LineSize +1 allows for the trailing null on C strings.

I would also suggest that you read your text into a single fixed buffer with some extra space and then use strcpy() to move it to your array. If your expected length is 50 chars, allocate at least 100 to this input buffer. This is to guard against lines that are longer than expected or lines that are missing EOL markers.