Problem With Using fgets()/gets()/scanf() After scanf() in C
scanf() is a library function in C. It reads standard input from stdin. fgets() is a library function in C. It reads a line from the specified stream and stores it into the string pointed to by the string variable. It only terminates when either:
- end-of-file is reached
- n-1 characters are read
- the newline character is read
1) Consider a below simple program in C. The program reads an integer using scanf(), then reads a string using fgets(),
x = 10, str =
Explanation: The problem with the above code is scanf() reads an integer and leaves a newline character in the buffer. So fgets() only reads newline and the string “test” is ignored by the program.
2) The similar problem occurs when scanf() is used in a loop.
a b q
Press q to quit Enter a character a Enter a character Enter a character b Enter a character Enter a character q
Explanation: We can notice that the above program prints an extra “Enter a character” followed by an extra newline. This happens because every scanf() leaves a newline character in a buffer that is read by the next scanf.
How to Solve the Above Problem?
- We can make scanf() to read a new line by using an extra \n, i.e., scanf(“%d\n”, &x) . In fact scanf(“%d “, &x) also works (Note the extra space).
- We can add a getchar() after scanf() to read an extra newline.
The corrected programs for the above points will be,
1) scanf() when there is fgets() after it:
x = 10, str = test
2) When scanf() is used in a loop:
a b q
Output: Press q to quit
Enter a character a Enter a character b Enter a character q
This article is contributed by Dheeraj Gupta. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.