Question

hello i am trying to write to a FILE in a wanted line number using c programming language
and for some unknown reasons it doesnt get written
this is my checking code:

int main()
{
    int x;
    int counter = 0;
    char buffer[MAX];
    FILE* fp = fopen("sale_day.txt","w");
    fprintf(fp,"5 orange 11\n");
    fprintf(fp,"4 pelephone 222\n");
    fprintf(fp,"3 mirs 4000\n");
    fprintf(fp,"2 cellcom 302\n");
    fprintf(fp,"1 tmobile 500\n");
    fclose(fp);
    fp = fopen("sale_day.txt","r+");
    while (counter < 2)
    {// jumping two rows
        fgets(buffer,MAX,fp);// i tried using fscanf which didnt help aswell
        counter++;
    }
    fflush(fp); // i tried with and without still doesnt work
    fputs("$",fp);
    fflush(fp); // i tried with and without still doesnt work
    fclose(fp);
}

i expect to get :

5 orange 11
4 pelephone 222
$ mirs 4000
2 cellcom 302
1 tmobile 500

for some reason it stays as the following in “sale_day.txt” file

5 orange 11
4 pelephone 222
3 mirs 4000
2 cellcom 302
1 tmobile 500

even tho when i debug it it shows a “$” instead of the 3 digit

thanks in advance for your help !

Answer 1

What are you expecting? When I run your code, I get:

5 orange 11
4 pelephone 222
$ mirs 4000
2 cellcom 302
1 tmobile 500

This is exactly right given what you’ve coded: read two lines (leaving you positioned at the third line), and write a $ char.

Note that file write operations overwrite existing file data, or append new data to the end of a file. They don’t insert data (which may have been the operation you’re expecting).