如何在.txt文件C中搜索特定的字符串和整数并使用它们？

Question

This code is a small learning experience about File I/O which i can't quite finish yet:

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int main()
{
    FILE *fP;

    char so_name[64];
    char user_name[64];
    int number;
    char continue_button;

    time_t t;

    system("TITLE Love-0-meter");
    system("COLOR 4D");

    srand((unsigned) time(&t));
    number = (rand() %100);

    printf("Hi and welcome to the love-o-meter, please fill in the details and see how much you and your SO"
       " love each other!\n\nHave you used this program before?(Y/N)");
    do
    {
        scanf(" %c", &continue_button);

    }while(continue_button != 'n' && continue_button != 'N' && continue_button != 'Y' && continue_button != 'y');

    system("CLS");
    printf("Enter your SO's name: ");
    scanf(" %s", so_name);
    printf("Enter your name: ");
    scanf(" %s", user_name);
    printf("\n%s and %s, you love each other %d%%", so_name, user_name, number);

    if(continue_button == 'N' || continue_button == 'n')
    {
        fP = fopen("Love-o-meter.txt", "w");
    }
    else
    {
        fP = fopen("Love-o-meter.txt", "a");
    }
    fprintf(fP, "%s %s %i\n", so_name, user_name, number);
    fclose(fP);

    return 0;
}

Basically the user must enter 2 names in and be saved in a .txt file along with a random number. But before the names get saved the program must check if they've been used before in the same order and are already in the file. If they have indeed been used before, the program must not generate a new number but use the one saved together with the 2 names and print it out on the screen.

I've been reading all day but i just can't figure out how and what to implement to be able the program to read previously saved names and numbers and use them if it finds a match.

Answer 1

You can save your position in file, scan it from beginning and then return to saved position.

char name1[256], name2[256];
int val;
size_t pos = ftell(fP);
rewind(fP);
while(fscanf(fp, "%s %s %d", name1, name2, &val) == 3) {
    // compare everything you need
}
fseek(fP, pos, SEEK_SET)

I hope I understood you right :)

Answer 2

What you want to do is to parse the file. In order to do this with strings in a text file, you need some way of knowing where to find names and results stored for the names.

As the previous answer proposed, using positions is something you should really look into. In addition to this, perhaps you want to separate names and results with a space or a character, and each new entry with a newline. You can use this, combined with a saved position, to tell at what entry you are, and whether you are reading a name or a result.

Further on, you should probably do some reading on the 'fopen' documentation, eg this

I do hope this was what you looked for.

Answer 3

I've been reading all day but i just can't figure out how and what to implement to be able the program to read previously saved names and numbers and use them if it finds a match.

You already described correctly what needs to be done. In order to do it, you have to

• open the file in a mode which allows reading ( a+ instead of a )
• read the saved names and numbers eg with fscanf()
• compare them to the entered names with strcmp()
• assign the saved number if the names match

- so change

    printf("\n%s and %s, you love each other %d%%", so_name, user_name, number);

    if(continue_button == 'N' || continue_button == 'n')
    {
        fP = fopen("Love-o-meter.txt", "w");
    }
    else
    {
        fP = fopen("Love-o-meter.txt", "a");
    }
    fprintf(fP, "%s %s %i\n", so_name, user_name, number);

to

    if(continue_button == 'N' || continue_button == 'n')
    {
        fP = fopen("Love-o-meter.txt", "w");
    }
    else
    {
        char so_used[64];
        char user_used[64];
        int nuused;
        fP = fopen("Love-o-meter.txt", "a+");   // append + read
        while (fscanf(fP, "%s %s %i\n", so_used, user_used, &nuused) == 3)
            if (!strcmp(so_used, so_name) && !strcmp(user_used, user_name))
            {
                number = nuused;
                goto out;
            }
    }
    fprintf(fP, "%s %s %i\n", so_name, user_name, number);
out:
    printf("%s and %s, you love each other %d%%\n", so_name, user_name, number);