Thread: Reading, Storing and Writing a file in C

Hello,

So this is the task i am trying to complete. Take a text file and read it into C. read specifically the last 3 columns of the file and store them as arrays for later calculation. How can i just scan those particular columns and bypass the rest. Attached is the text file

I also wanted to write a file of just those 3 columns to as a check that i have done it correctly

This is what i started writing as a general set up

Code:

#include <stdio.h>
#include <math.h>
#include <quadmath.h>
typedef __float128 real;
typedef __float128 doublereal;
#include <stdlib.h>


double LDout[81], LDout2[81], LDout3[81]; 

FILE *fptr1, *fptr2;

//Main function
int main()
{

//Open/Reads file Surrogate Run_Finite_Difference_81.in
    fptr1 = fopen("Surrogate Run_Finite_Difference_81.in","r"); 

//Open/Writes file Surrogate Run_Finite_Difference_81.out

    fptr2 = fopen("Surrogate Run_Finite_Difference_81.out","w");  




//Close Finite_Difference.in file
    fclose(fptr1);
//Close Finite_Difference.out file
    fclose(fptr2);
return 0;
}

I am fairly new to C so any help or sudo code would be appreciated.

Hey! thank you for the tip! I extracted what i need to exactly! For now this will suffice so i can move on with other calculation. But i do want to put it into a loop so it looks cleaner but im not to sure how i'll do that yet. If you have any more tips that would be great! Thank you again

Code:

#include <stdio.h>
#include <math.h>
#include <quadmath.h>
typedef __float128 real;
typedef __float128 doublereal;
#include <stdlib.h>

char   line[1500];
int    i;
double LDout[80], LDout2[80], LDout3[80];

int main()
{
fptr3 = fopen("Surrogate Run_Finite_Difference_81.in","r");   //Open/Reads file Surrogate Run_Finite_Difference_81.in
    fptr4 = fopen("Surrogate Run_Finite_Difference_81.out","w");  //Open/Writes file Surrogate Run_Finite_Difference_81.out


    printf("Input:\n\n");      //print to screen


// Reads the LD labels
    fscanf(fptr3, "%s %*s %*s %*s %*s %*s %*s %*s %*s %*s %*s %*s %*s %*s %*s %*s %*s %*s %*s %*s %*s %*s %*s %*s %*s %*s %*s %*s %*s %*s %*s %*s %*s %*s %*s %*s %*s %*s %*s %*s %*s %s %s %s\n", line, LDout, LDout2, LDout3);
    fprintf(fptr4,"%s %s %s %s\n", line, LDout, LDout2, LDout3);
    printf("%s %s %s %s\n", line, LDout, LDout2, LDout3);


// Reads the Values for LDout, LDout2 and LDout3 from Surrogate Run_Finite_Difference_81.in
    for (i=0; i<=80; i++) {
        fscanf(fptr3, "%s %*lf %*lf %*lf %*lf %*lf %*lf %*lf %*lf %*lf %*lf %*lf %*lf %*lf %*lf %*lf %*lf %*lf %*lf %*lf %*lf %*lf %*lf %*lf %*lf %*lf %*lf %*lf %*lf %*lf %*lf %*lf %*lf %*lf %*lf %*lf %*lf %*lf %*lf %*lf %*lf %lf %lf %lf\n", Doe, &LDout[i], &LDout2[i], &LDout3[i]);
        fprintf(fptr4,"%s %.16lg %.16lg %.16lg\n", Doe, LDout[i], LDout2[i], LDout3[i]);
        printf("%s %.16lg %.16lg %.16lg\n", Doe, LDout[i], LDout2[i], LDout3[i]);
    }

Not exactly how I'd do it, and hopefully I counted the number of columns correctly, but maybe something like the code below. I'll leave it to you to add error checking (check for end of file etc etc). The numbers 80 and 41 probably shouldn't be hardcoded, it'd be better to have #define SKIP_COLUMN_COUNT 41 and then use j < SKIP_COLUMN_COUNT in the loop, for example

Code:

#include <stdio.h>
#include <errno.h>

int main(void)
{
    char   line[1500];
    int    i;
    double LDout, LDout2, LDout3;
    
    FILE *fptr3 = fopen("Surrogate Run_Finite_Difference_81.in","r");   //Open/Reads file Surrogate Run_Finite_Difference_81.in
    if (!fptr3) {
        perror("Error");
        return 1;
    }
    
    fgets(line, sizeof line, fptr3);    // Read the labels
        
    for (i = 0; i <= 80; i++) {
        for (int j = 0; j < 41; j++) {
            fscanf(fptr3, " %*s");
        }
        fscanf(fptr3, " %lf %lf %lf", &LDout, &LDout2, &LDout3);
        printf("%f %f %f\n", LDout, LDout2, LDout3);
    }
    
    fclose(fptr3);
    
    return 0;
}

Hello, you have helped me tremendously with this forum. I do have another question if you would be able to assist? would be greatly appreciated. Link is below. Its a add on to what i was doing here. The j term is not necessarily 41, it could be a lower value so i have to determine this be counting the number of columns from the text file.

How to count the amount of columns or elements in my text file.