C Library - fscanf() function

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The C library int fscanf(FILE *stream, const char *format, ...) function reads formatted input from a stream. It is part of the Standard I/O library and is defined in the <stdio.h> header. This function allows for extracting and parsing data from a file according to a specified format.

Syntax

Following is the C library syntax of the fscanf() function −

int fscanf(FILE *stream, const char *format, ...);

Parameters

This function uses various parameter to works on file handling &minus-

• *FILE stream : This is a pointer to the FILE object that identifies the input stream from which data is to be read.
• *const char format:This is a C string that contains a format string composed of conversion specifiers. These specifiers determine the type and format of the data to be read.
• ... (ellipsis):This represents a variable number of additional arguments that point to the locations where the parsed values will be stored. Each argument must correspond to a format specifier in the format string.

Return value

The fscanf function returns an integer value representing the number of input items successfully matched and assigned. If the input ends before the first matching failure or if an error occurs, EOF (End Of File) is returned.

Example 1: Reading Integer and String

The below code reads an integer and a string from the file and prints them.

Following is the illustration of the C library fscanf() function.

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

int main() {
   const char *filename = "example1.txt";
   FILE *file = fopen(filename, "r");

   // If the file does not exist, create and write initial data to it
   if (file == NULL) {
       file = fopen(filename, "w");
       if (file == NULL) {
           perror("Error creating file");
           return 1;
       }
       fprintf(file, "123 HelloWorld\n");
       fclose(file);
       file = fopen(filename, "r");
       if (file == NULL) {
           perror("Error opening file");
           return 1;
       }
   }

   int number;
   char word[50];

   if (fscanf(file, "%d %49s", &number, word) == 2) {
       printf("Number: %d, Word: %s\n", number, word);
   } else {
       printf("Failed to read data from file.\n");
   }

   fclose(file);
   return 0;
}

Output

The above code produces following result−

Number: 123, Word: HelloWorld

Example 2: Reading Multiple Floating Point Numbers

The below code reads three floating-point numbers from the file and prints them.

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

int main() {
   const char *filename = "example2.txt";
   FILE *file = fopen(filename, "r");

   // If the file does not exist, create and write initial data to it
   if (file == NULL) {
       file = fopen(filename, "w");
       if (file == NULL) {
           perror("Error creating file");
           return 1;
       }
       fprintf(file, "3.14 2.718 1.618\n");
       fclose(file);
       file = fopen(filename, "r");
       if (file == NULL) {
           perror("Error opening file");
           return 1;
       }
   }

   float num1, num2, num3;

   if (fscanf(file, "%f %f %f", &num1, &num2, &num3) == 3) {
   if (fscanf(file, "%f %f %f", &num1, &num2, &num3) == 3) {
       printf("Numbers: %.2f, %.2f, %.2f\n", num1, num2, num3);
   } else {
       printf("Failed to read data from file.\n");
   }

   fclose(file);
   return 0;
}

Output

After execution of above code, we get the following result

Numbers: 3.14, 2.72, 1.62

Example 3: Reading Date from File

The below code reads a date in DD/MM/YYYY format and prints it in DD-MM-YYYY format.

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

int main() {
   const char *filename = "example3.txt";
   FILE *file = fopen(filename, "r");

   // If the file does not exist, create and write initial data to it
   if (file == NULL) {
       file = fopen(filename, "w");
       if (file == NULL) {
           perror("Error creating file");
           return 1;
       }
       fprintf(file, "23/05/2024\n");
       fclose(file);
       file = fopen(filename, "r");
       if (file == NULL) {
           perror("Error opening file");
           return 1;
       }
   }

   int day, month, year;

   if (fscanf(file, "%d/%d/%d", &day, &month, &year) == 3) {
       printf("Date: %02d-%02d-%04d\n", day, month, year);
   } else {
       printf("Failed to read data from file.\n");
   }

   fclose(file);
   return 0;
}

Output

The output of the above code is as follows −

Date: 23-05-2024