scanf() and fscanf() in C

In C language, scanf() function is used to read formatted input from stdin. It returns the whole number of characters written in it otherwise, returns a negative value.

Syntax:

Time Complexity: O(n)

Auxiliary Space: O(n) where n is the length of input.

Many of us know the traditional uses of scanf. Well, here are some of the lesser-known facts

How to read only a part of the input that we need?
For example, consider some input stream that contains only characters followed by an integer or a float. And we need to scan only that integer or float.

Example:

Now, assume we don’t know what the preceding characters are but we surely know that the last value is an integer. How can we scan the last value as an integer?

The below solution works only if the input string has no spaces. For example,

Input

Output

Explanation : The %*s in scanf is used to ignore some input as required. In this case, it ignores the input until the next space or newline. Similarly, if you write %*d it will ignore integers until the next space or newline.

General use of scanf( ):

Input

Output

The above fact may not seem like a useful trick at the first glance. In order to understand its usage, let us first see fscanf().

fscanf Function in C

Tired of all the clumsy syntax to read from files? well, fscanf comes to the rescue. This function is used to read the formatted input from the given stream in the C language.

Syntax:

fscanf reads from a file pointed by the FILE pointer (ptr), instead of reading from the input stream.

Return Value: It returns zero or EOF, if unsuccessful. Otherwise, it returns the number of items successfully assigned.

Time Complexity: O(n)

Auxiliary Space: O(n) where n is the length of the input.

Example 1: Consider the following text file abc.txt

Now, we want to read only the city field of the above text file, ignoring all the other fields. A combination of fscanf and the trick mentioned above does this with ease

Output

Example 2: Consider the following binary file program.bin

To read all values of n1, n2 & n3 of the bin, we are using fscanf()

Output

Let us see the differences in a tabular form -:

scanf(const char *format, …)

fscanf(FILE *stream, const char *format, …)

It takes three parameters that are -:

Whitespace character , Non-whitespace character,Format specifiers