Wrong gcc behaviour with lambda

Question

By compiling this:

#include <iostream>
#include <sstream>

std::string makeList (std::string sep)
{
    auto makeItem = [&] (std::string item)
    {
        static char count = '0';
        return (++count, count) + sep + item + '\n';
    };

    return makeItem ("first") + makeItem ("second") + makeItem ("third");
}

int main() 
{
    std::cout << makeList (". ");
}

with gcc (5.4.0, c++11 flag) the output is this:

3. first
2. second
1. third

while the correct output, which clang (3.8, c++11 flag) gets, is:

1. first
2. second
3. third

Is there a particular reason for this behaviour?

Answer 1

According to cppreference :

Order of evaluation of the operands of almost all C++ operators (including the order of evaluation of function arguments in a function-call expression and the order of evaluation of the subexpressions within any expression) is unspecified. The compiler can evaluate operands in any order, and may choose another order when the same expression is evaluated again.

There is no right or wrong here, GCC evaluates right-to-left and clang left-to-right