C++ is really fun to work with, but it does make it really easy sometimes to shoot yourself in the foot.
Consider this program:
#include <iostream>
int main() {
int foo = 1.5;
std::cout << foo << "\n";
return 0;
}Obviously this outputs 1, not 1.5, and with clang++ by default you get a warning like this:
test.cpp:4:12: warning: implicit conversion from 'double' to 'int' changes value from 1.5 to 1 [-Wliteral-conversion]
int foo = 1.5;
~~~ ^~~
So far, this makes total sense.
Let’s now modify this program slightly:
#include <iostream>
int main() {
- int foo = 1.5;
+ int foo = 3 * 1.5;
std::cout << foo << "\n";
return 0;
}This outputs 4, but you don’t get any warning anymore! Only when enabling -Wconversion you get this:
test.cpp:4:14: warning: implicit conversion turns floating-point number into integer: 'double' to 'int' [-Wfloat-conversion]
int foo = 3 * 1.5;
~~~ ~~^~~~~
Still makes sense to disable this warning by default, I think, because there is likely a lot of legacy code depending on these implicit conversions. However, this warning is not included in -Wall or -Wextra in both clang and g++! So I was hit by this and spent time debugging, even though I already had turned warnings up as much as possible.
From now on, -Wconversion is always going into my build flags.