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.
That is ,
Input: “this is the value 100”,
Output: value read is 100
Input : “this is the value 21.2”,
Output : value read is 21.2
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?
Below solution works only if input string has no spaces.
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 new line. Similarly if you write %*d it will ignore integers until the next space or new line.
The above fact may not seem as an useful trick at the first glance. Inorder to understand its usage, let us first see fscanf().
fscanf() : Tired of all the clumpsy syntax to read from files? well, fscanf comes to the rescue.
int fscanf(FILE *ptr, const char *format, ...)
fscanf reads from a file pointed by the FILE pointer (ptr), instead of reading from the input stream.
Consider the following text file abc.txt
NAME AGE CITY abc 12 hyderbad bef 25 delhi cce 65 bangalore
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
CITY hyderbad delhi bangalore
Exercise: Count the number of words, characters and lines in a file using fscanf!
This article is contributed by Nikhil Chakravartula. If you like GeeksforGeeks and would like to contribute, you can also write an article and mail your article to email@example.com. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
- Inbuilt library functions for user Input | scanf, fscanf, sscanf, scanf_s, fscanf_s, sscanf_s
- Problem with scanf() when there is fgets()/gets()/scanf() after it
- scanf("%[^\n]s", str) Vs gets(str) in C with Examples
- Difference between scanf() and gets() in C
- Why to use fgets() over scanf() in C?
- Use of & in scanf() but not in printf()
- Cin-Cout vs Scanf-Printf
- Why "&" is not used for strings in scanf() function?
- Return values of printf() and scanf() in C/C++
- OpenGL program for simple Animation (Revolution) in C
- OpenGL program for Simple Ball Game
- tgamma() method in C/C++ with Examples
- Modulo Operator (%) in C/C++ with Examples
- fpclassify() method in C/C++ with Examples