fscanf not reading next line [FIXED]

In this article, we have explored why a C++ code using fscanf cannot read next line and how to fix it by using getline() and sscanf() in C++ by keeping the syntax same. We have demonstrated this with C++ code examples.

Table of contents:

1. Understanding the problem and fix
2. fscanf not reading next line
3. Fix with C++ code

Understanding the problem and fix

This is the major problem with using fscanf to read data from a text file. The issue is fscanf does not recognize new line character (\0).

The fix is to:

• Read each line one by one using getline()
• Extract data from each line using sscanf() just like fscanf() (same syntax)

fscanf not reading next line

Let the file (opengenus.txt) be of the following format:

10, 53, 101
-9, 33, 10
44, 2, 1
1, 2, 3
5, 0, 5
...

#include <string.h>
#include <cstdlib>

int main(int argc, char** argv) {
    FILE* my_file = fopen("opengenus.txt", "r");
    int data[100][3];

    for(int count = 0; count < 100; count++) {
        int got = fscanf(my_file, "%d,%d,%d", data[count][0], 
                  data[count][2], data[count][2]);
    }
}

The issue with the above C++ code is that fscanf cannot read the next line and reads only the first line of the file.

Fix with C++ code

Following is the correct C++ code:

#include <string.h>
#include <cstdlib>

int main(int argc, char** argv) {
    FILE* my_file = fopen("opengenus.txt", "r");
    char* line = NULL;
    size_t len = 0;
    int data[100][3];

    for(int count = 0; count < 100; count++) {
        size_t read = getline(&line, &len, my_file);

        int got = sscanf(line, "%d,%d,%d", data[count][0], 
                  data[count][2], data[count][2]);
    }
}

With this article at OpenGenus, you must have the complete idea of how to fix the problem of fscanf not reading next line.