Walter Brown's cool technique for reading files

How do you write a loop to do something with each line of a file? One common way:

string s;
while (getline(file, s)) { /* do something */ }


This technique has the small disadvantage of separating the definition of s from the loop that uses it, and therefore of having the value of s hang around longer than needed.

Walter Brown, from the Fermi National Accelerator Laboratory and a member of the C++ committee, once suggested to me the following elegant technique:

for (string s; getline(file, s);) { /* do something */ }


Once seen, this technique seems obvious; but good ideas often seem that way.

Posted by Andrew Koenig at 04:15 PM  Permalink