How to convert from char to int in C reading from a file?

Question

I am trying to read a file in C which has four numbers per line which represents coordinates of two points and then I am trying to find the distance between the two points. For this, I am reading the file lines one by one and I am getting it as a char array. Below is what I have done.

Output function which I am calling from read()

void output(char *buff){
    int co1,co2,co3,co4;
    co1 = atoi(buff[0]);
    co2 = atoi(buff[2]);
    co3 = atoi(buff[4]);
    co4 = atoi(buff[6]);
    printf("(%d,%d) lies on the %s,(%d,%d) lies on the %s, distance is %f.\n",co1,co2,quadrant(co1,co2),co3,co4,quadrant(co3,co4),distance(co1,co2,co3,co4));

}

Read function which I am calling from main.

int read(){
    FILE *file;
    char buff[255];
    file = fopen("point.dat", "r");
    while(!feof(file)){
        fgets(buff,255,file);
        output(buff);
    }
    return !feof(file);
}

Main function

int main()
{
    read();
    return 0;

}

But while doing so, I am getting below error.

[Error] invalid conversion from 'char' to 'const char*' [-fpermissive]

The data of point.dat is

0 0 3 4
-1 -4 5 6
-1 3 -1 -2
4 -5 -5 -6
3 5 -6 5
0 5 5 5 
-5 0 0 -5

How can I convert char to array in output function? I tried stoi function too, but I got error that "stoi is not in scope"

Answer 1

In your output() function, buff[i] is only one char which is not a string (char*) for atoi(). You should use strtok() to buff into tokens using the delimiter space and then pass each token to atoi().