how to read scanf with spaces

Question

I\'m having a weird problem

i\'m trying to read a string from a console with scanf()

like this

scanf(\"%[^\\n]\",string1);

Answer 1

I'll bet your scanf call is inside a loop. I'll bet it works the first time you call it. I'll bet it only fails on the second and later times.

The first time, it will read until it reaches a newline character. The newline character will remain unread. (Odds are that the library internally does read it and calls ungetc to unread it, but that doesn't matter, because from your program's point of view the newline is unread.)

The second time, it will read until it reaches a newline character. That newline character is still waiting at the front of the line and scanf will read all 0 of the characters that are waiting ahead of it.

The third time ... the same.

You probably want this:

if (scanf("%99[^\n]%*c", buffer) == 1) {

Edit: I accidentally copied and pasted from another answer instead of from the question, before inserting the %*c as intended. This resulting line of code will behave strangely if you have a line of input longer than 100 bytes, because the %*c will eat an ordinary byte instead of the newline.

However, notice how dangerous it would be to do this:

scanf("%[^n]%*c", string1);

because there, if you have a line of input longer than your buffer, the input will walk all over your other variables and stack and everything. This is called buffer overflow (even if the overflow goes onto the stack).