fscanf repeating characters

Question

When data is read from a text file with fscanf , data from the next column is appended to the string data. How can I get only the data from that column?

Input file: student.txt

Donald 23 KOR CE
Mitchell 24 USA EE
John 22 KOR CE

Output:

Donald 23 KORCE CE
Mitchell 24 USAEE EE
John 22 KORCE CE

In the data in the first row, the country should be KOR , but it comes out as KORCE .

My code so far:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define MAX_LINE_LENGTH 100

typedef struct
{
  char name[20];
  int age;
  char country[3];
  char dept[2];
} STUDENT;

int main()
{
  int i = 0;
  STUDENT student[15];

  // Initialize the student array
  for (i = 0; i < 15; i++) {
    memset(student[i].name, 0, sizeof(student[i].name));
    student[i].age = 0;
    memset(student[i].country, 0, sizeof(student[i].country));
    memset(student[i].dept, 0, sizeof(student[i].dept));
  }

  // Open the file for reading
  FILE *fp = fopen("student.txt", "r");
  if (fp == NULL)
  {
    puts("Error: Could not open file 'student.txt'");
    return 1;
  }

  // Read the file line by line
  char line[MAX_LINE_LENGTH];
  while (fgets(line, MAX_LINE_LENGTH, fp) != NULL) {
    // Parse the line and fill the structure
    if (sscanf(line, "%s %d %s %s\n", student[i].name, &student[i].age, student[i].country, student[i].dept) != 4) {
      printf("Error: Invalid data in file 'student.txt'\n");
      return 1;
    }

    // Print the structure
    printf("Name: %s\n", student[i].name);
    printf("Age: %d\n", student[i].age);
    printf("Country: %s\n", student[i].country);
    printf("Dept: %s\n", student[i].dept);

    i++;
  }

  // Close the file
  fclose(fp);

  return 0;
}

I want the country name to read normally as 3 characters.

Answer 1

No widths leads to undefined behavior

The data was too large for student[i].country[3] , causing a buffer overflow as format lacked a width to prevent that. The width for "%s" needs to be 1 less than the buffer size. Recall the "%s" appends a null character after storing input text. Had OP used widths , the trouble would rapidly have made itself known.

The "\n" at the end of the format serves scant useful purpose.

// sscanf(line, "%s %d %s %s\n", 
sscanf(line, "%19s %d %2s %1s", 
    student[i].name, &student[i].age, 
    student[i].country, student[i].dept)

Certainly though OP wants larger, by 1, buffers.

---

Alternative error detection

Use "%n" to save the scanning offset, if it got that far. It also detects if junk text followed the department .

  while (i < 15 && fgets(line, MAX_LINE_LENGTH, fp) != NULL) {
    int n = 0;
    sscanf(line, "%19s %d %2s %1s &n", 
        student[i].name, &student[i].age, student[i].country,
        student[i].dept, &n);
    if (n == 0 || line[n]) {
      printf("Error: Invalid data <%s> in file 'student.txt'\n", line);
      return 1;
    }
    ...
  }

---

It is even reasonable to use a width with "%d" , like "%3d" to limit the age range to -99 to 999. This would help catch some pathologic values and prevent overflow.

Input data is evil. Do not trust it until vetted.

---

Some insights on US names

Answer 2

Thank you for your suggestions. But I'm sorry that the way you suggested didn't solve it. Resizing "country[3]" to "country[10]" solved the problem, but I'm still not sure why.