Comments on: Difference between “vector v” and “vector v()” http://efesx.com/2009/08/11/difference-between-vector-v-and-vector-v/ Technical & low level Mon, 30 Apr 2012 17:39:06 +0000 hourly 1 http://wordpress.org/?v=3.3.2 By: Or http://efesx.com/2009/08/11/difference-between-vector-v-and-vector-v/#comment-7 Or Tue, 20 Apr 2010 20:59:25 +0000 http://cpptalk.wordpress.com/?p=3#comment-7 Yes, it's called The Most Vexing Parse, and it is a really vexing one. When you say vector v2() you are actually importing an external function(named v2 and that returns a vector of ints and has no parameters) from another translation unit. This can be even more vexing if you write: Suppose you want to read a file which his name stored in a variable filename, and copy it directly into a new vector: [sourcecode language="cpp"] vector<int> v(istream_iterator<int>(filename), istream_iterator<int>()); [/sourcecode] Although it is somehow not trivial example, that will be parsed by the vexing c++ compiler as a function declaration (because the parenthesis can be omitted to get a function declaration), not a vector initialization. to remedy the situation we have to do something like the following: [sourcecode language="cpp"] istream_iterator<int> begin(filename); istream_iterator<int> end; vector<int> v(begin, end). [/sourcecode] Thanks! Yes, it’s called The Most Vexing Parse, and it is a really vexing one. When you say vector v2() you are actually importing an external function(named v2 and that returns a vector of ints and has no parameters) from another translation unit.
This can be even more vexing if you write:
Suppose you want to read a file which his name stored in a variable filename, and copy it directly into a new vector:

vector<int> v(istream_iterator<int>(filename), istream_iterator<int>());

Although it is somehow not trivial example, that will be parsed by the vexing c++ compiler as a function declaration (because the parenthesis can be omitted to get a function declaration), not a vector initialization. to remedy the situation we have to do something like the following:

istream_iterator<int> begin(filename);
istream_iterator<int> end;
vector<int> v(begin, end).

Thanks!

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