CODEWITHSUNDEEP
carrays
Ðiffëřëņt ĞîRl
Ðiffëřëņt ĞîRl

Reputation: 39

read a file and save as a matrix

i have a file like that : 

1 100
2 200
3 300
4 400
1

i want to save it as a matrix and i want to save NULL if there is no second number !

i tried to write the program but it does not work correctly ! 

#include<stdio.h>
int main() {
int k=0 ,i,j , arr[100][100];
FILE *in= fopen("file.txt","r");
char line[1000]; 
while(fgets(line,1000,in) !=NULL) k++;
fgets(line,1000,in);
for (i=0;i<k;i++){
    for (j=0;j<2;j++){
        int tmp ;
        fscanf(in ,"%d", &tmp) ;
        arr[i][j] = tmp ;
    }
}
fclose(in);
return 0; }

Upvotes: 0

Views: 83

Answers (1)

Some programmer dude
Some programmer dude

Reputation: 409166

Two major problems:

The first is that the first loop will read all lines, even the one with the single number on the line. That means the lonely fgets call will not do anything, and more importantly that the value of k will be wrong.

The second problem is that once you read all data from the file, you don't go back to the beginning of the file, instead you continue to try and read from beyond the end of the file.

The first problem can be solve by skipping the second fgets call, and decreasing k by one.

The second problem can be solved by calling rewind after you counted the number of lines.

Also when you actually read the numbers, you don't need the inner loop, just do e.g.

scanf("%d %d", &arr[i][0], &arr[i][1]);

Actually, you don't need the first line-counting loop at all, you can do it all in a single loop, by using fgets and sscanf and then checking the return value of sscanf. So your program could look something like

#include <stdio.h>

int main(void)
{
    int values[100][2];
    FILE *input = fopen("file.txt", "r");
    size_t entries = 0;

    if (input != NULL)
    {
        char buffer[40];
        while (fgets(buffer, sizeof(buffer), input) != NULL && entries < 100)
        {
            int res = sscanf(buffer, "%d %d", &values[entries][0], &values[entries][1]);
            if (res <= 1 || res == EOF)
            {
                // Read the last line with only one number, or an error happened
                values[entries][0] = 0;
                values[entries][1] = 0;
                break;
            }

            ++entries;
        }

        if (ferror(input))
        {
            printf("Error reading file\n");
        }

        fclose(input);
    }

    // All done, the number of "records" or "entries" is in the variable entries

    // Example code: print the values
    for (size_t i = 0; i < entries; ++i)
        printf("Line %d: %d %d\n", i + 1, values[i][0], values[i][1]); 

    return 0;
}

Upvotes: 2

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