Why is My Program Unable To Read the Data from My File

Question

My Program Works Mostly, except for When I try to read the Total Data that was Entered

#include <stdio.h>
#include <string.h>
#define bufferSize 300
char name[50], gift[50], list[300], end[50], *result;
int i;
int main()
{
    FILE *appendPlace = fopen("NamesAndGifts.txt", "a");
    FILE *readData = fopen("NamesAndGifts.txt", "r"); //my place for reading data
    printf("This is a Gift Entering System for 3 People Only\nThe Name of the Person then their Gift Description will be taken\nThe Gift Description is Basically the Gift Name");
    while (strcmp(end, "END") != 0) {
        printf("\nEnter Name of Person %d or type 'END' to Exit Sequence\n", i + 1);
        scanf("%s", &end);
        if (strcmp(end, "END") != 0) {
            strcpy(name, end);
            printf("Now Enter Gift Description (Gift Name) of Person %d\n", i + 1);
            scanf("%s", &gift);
            strcat(list, "\n");
            strcat(list, "Name: ");
            strcat(list, name);
            strcat(list, "\n");
            strcat(list, "Gift: ");
            strcat(list, gift);
            strcat(list, "\n");
        }
        i++;
    }
    printf("The Gift Entering System (Names and their respective Gifts) is Below:\n");
    printf("%s", list);

    fputs(list, appendPlace);
    fclose(appendPlace);
    //below I attempt to read file Data to be able to print file's Data into running program
    fscanf(readData, "%s", result);
    printf("\n\n\n\n\n\n\nTotal Data in File Below:\n%s", result);
    fclose(readData);
}

I tried out doing just file reading, and it seems that reading from the file like that can only read data that is not separated by (space bar) or (enter) Is there a way to Solve this?

@AnttiHaapala there is no need to be preceded by a `strcpy`, a NUL terminated is enough, and `list`, as global, is already NUL terminated — David Ranieri, Oct 11 '19 at 22:01
You do realise that everything in the while loop works fine to my objectives. My only problem like I stated was that I cannot get to properly read the file in which the data was appended to -_- — The Bomb Squad, Oct 11 '19 at 22:01
`fscanf` with the `%s` format specifier scans until it meets the first white space character. Aside, don't use the `&` address-of operator with the `%s` format. — Weather Vane, Oct 11 '19 at 22:04
Can you tell us a bit more about what the problem is and what you are trying to achieve? Edit: Maybe give us an example of input and correct/incorrect output? — kyriakosSt, Oct 11 '19 at 22:06
You can read *all of the file data* with `fread` and terminating the string properly. — Antti Haapala -- Слава Україні, Oct 11 '19 at 22:06
... and the pointer `*result` has **no memory** allocated to it. So `fscanf(readData, "%s", result);` has *undefined behaviour*. — Weather Vane, Oct 11 '19 at 22:08
ok @kyriakosSt so i have my program, a file already made called "NamesAndGifts.txt", my program properly appends to the file the data that I want, also how i want, but the problem is, on the black screen that the compiled c program runs on, it is not showing me the data there — The Bomb Squad, Oct 11 '19 at 22:08
@WeatherVane thanks for the format change of result, but it only shows "Name: " — The Bomb Squad, Oct 11 '19 at 22:14
As I also mentioned, `"Name: "` has a space in it, which ends the scan. Also don't overlook my other comment, about there being **no valid memory** to read the data into. — Weather Vane, Oct 11 '19 at 22:15
What do you mean "no valid memory"? Isn't scanning how you apply data to a variable in c? — The Bomb Squad, Oct 11 '19 at 22:16
`char *result;` is a pointer. That's all it is, an *uninitialised* pointer. You have to allocate memory to it, enough to contain the entire file. — Weather Vane, Oct 11 '19 at 22:18
I turned it into result[1000] so yea i did that, but it only reads "Name: ". The Question is how to get around that? — The Bomb Squad, Oct 11 '19 at 22:19
[This comment](https://stackoverflow.com/questions/58348894/why-is-my-program-unable-to-read-the-data-from-my-file#comment103052963_58348894) suggests one way. Using the array: `size_t bytes = fread(result, 1, (sizeof result) - 1, readData); result[bytes] = 0;` — Weather Vane, Oct 11 '19 at 22:21
Let us [continue this discussion in chat](https://chat.stackoverflow.com/rooms/200740/discussion-between-the-bomb-squad-and-weather-vane). — The Bomb Squad, Oct 11 '19 at 22:34

score 2 · Accepted Answer · answered Oct 11 '19 at 22:29

So there are 2 problems in your code.

result has no memory allocated to it. Since it is a global variable, it is initialized to 0, aka a NULL pointer. So your scanf() sees that and the reading fails and so does printf() and prints "(null)". The solution there is to allocate memory in result either by making it a static array or by using malloc().
Even if you fix the first problem, however, it will still not work as expected as fscanf() will stop reading input after the first whitespace is encountered. Since you want the whole (file) input to be read, you have four options:
- Read character by character (not advisable for performance reasons but perhaps the easiest to implement)
- read line by line (fairly a standard way)
- read chunk by chunk given some pre-allocated buffer or
- read the whole file at once (not advised for big files)

The functions to use are fgetc(), getline(), fread(). Additionally, you can find the size of the file by following this question

fseek(readData, 0, SEEK_SET); fread(result, 1001, 1, readData); printf("\n\n\n\n\n\n\nTotal Data in File Below:\n%s", result); fclose(readData); — The Bomb Squad, Oct 11 '19 at 22:38
That is the data at the end of my code that solved the problem. Thanks thought guys. I was troubled with displaying the file's data for quite a while now — The Bomb Squad, Oct 11 '19 at 22:40

Why is My Program Unable To Read the Data from My File

1 Answers1