识别C或C ++中的空格分隔符和换行符

Question

In programming competitions, often the input given is of the form:

1 3 5 544
4 
2 3 22
2423 
2 

where there are multiple lines of integers delimited by a space. I've been trying to figure out how to read these input in C or C++ but could never really get it to work. Solutions that I've found on the web either use scanf or getline (or fget) but whenever I tried, they either failed to recognize the newline character or, when I tried to use them in conjunction with a for loop, the first iteration wasn't executed.

How do the competitive programmers read this type of input?

Answer 1

Read the stream line-by-line using getline() (suggested the "getline function", which works with std::string , not the "getline method of istream").

Then to extract the numbers use std::istringstream initialized with a string read by getline() call.

Answer 2

In competentive programming - don't use C++ input at all - it's too slow and it will reflect on your times badly (especially if expected solution is in O(n) or faster). Program specifications are usually created in such a way, that trivial scanf will do the job (intentionally, so you can focus on algorithm instead of reading input). Your problem is that probably you want to parse whitespace and don't know how to do this (with scanf - you don't need to). For example, let's parse multiple lines containing two integers separated by space:

int x, y;
while (foo) {
    scanf("%d %d", &x, &y);
}

This will work just fine, you don't need to worry about newlines at all. If you will get into situation, that scanf is too slow (it might be in competitions) - you will probably need to create your own dedicated parsing function by calling getchar and processing input byte by byte.