std::chrono doesn't work if passing a variable

Question

I came across a weird error with std::chrono, If I do something like this:

TimeHandling time(std::chrono::milliseconds(1000 / 125));
time.start();

Everything is ok. But if instead I put the milliseconds value in a variable:

int mpl = 1000 / 125;
TimeHandling time(std::chrono::milliseconds(mpl));
time.start();

g++ throw this error:

 request for member ‘start’ in ‘time’, which is of non-class type ‘TimeHandling(std::chrono::milliseconds) {aka TimeHandling(std::chrono::duration<long int, std::ratio<1l, 1000l> >)}’

Does someone know why ?

Answer 1

The second version declares a function with a parameter called mpl

See http://en.wikipedia.org/wiki/Most_vexing_parse and https://stackoverflow.com/tags/most-vexing-parse/info

C++11 allows you to use braces to disambiguate initializations from declarations:

TimeHandling time{std::chrono::milliseconds(mpl)};

or, using braces for both initializations:

TimeHandling time{std::chrono::milliseconds{mpl}};