Read the next line of a file every time a function is called

Question

I have a text file with numbers on each line. I want to write a function in C that reads in the file and returns the next number in the file every time the function is called.

For example if I have these numbers:

100 
200 
300 
400

and a function called get_number(), if I call get_number() it will return 100, if I call it again, it will return 200, etc.

This is what I've written so far but every time the function is called, it always goes back to the first number in the text file.

int * get_number()
{

    FILE* file = fopen("random_numbers.txt", "r");
    char line[256];

    if (file==NULL) 
    {
        perror ("Error reading file");
    }
    else
    {
        fgets(line, sizeof(line), file);
        printf("%s", line);
    }

    return 0;
}

Answer 1

here's a version that does exactly that :

 int * get_number(long* pos)
{

    FILE* file = fopen("random_numbers.txt", "r");
    char line[256];

    if (file==NULL) 
    {
        perror ("Error reading file");
    }
    else
    {
        fseek(file , *pos , SEEK_CUR);
        fgets(line, sizeof(line), file);
        printf("%s", line);
    }
    *pos = ftell(file);
    return 0;
}

and you call it from main like this

long pos = 0;
get_number(&pos);

or better yet use a static variable

 int * get_number()
{
    static long pos = 0;
    FILE* file = fopen("random_numbers.txt", "r");
    char line[256];

    if (file==NULL) 
    {
        perror ("Error reading file");
    }
    else
    {
        fseek(file , pos , SEEK_CUR);
        fgets(line, sizeof(line), file);
        printf("%s", line);
    }
    pos = ftell(file);

    return 0;
}