What could be wrong with this construct?
if((auto idx = diff * 2) <= objRef.size()){
//do something
}
where diff is of type ptrdiff_t and objRef is of type std::vector.
The following compiler errors are generated for the above statement:
1 In file included from main.cpp:1:
2 ./bt.hpp:597:28: error: expected ')'
3 i
4 if((auto idx = diff * 2) <= objRef.size())
5 f((auto idx = diff * 2) <= objRef.size())
6 ^
7 ./bt.hpp:597:22: note: to match this '('
8 if((auto idx = diff * 2) <= objRef.size())
9 ^
10 ./bt.hpp:597:44: error: expected expression
11 if((auto idx = diff * 2) <= objRef.size())
12 ^
According to this answer: https://stackoverflow.com/a/7837092/159145 the contents of an if statement condition must be either an expression or a single-variable-declaration.
In your case, auto idx = diff * 2 is a single-variable-declaration, but because you combined it with <= objRef.size() the if's condition then ceases to be a single-variable-declaration, but it isn't an expression either because it includes a declaration - hence the compiler complains.
Change your code to compute idx before the if statement:
auto idx = diff * 2;
if( idx <= objRef.size() ) {
}
If you want to restrict the scope of idx then use an anonymous-scope:
{
auto idx = diff * 2;
if( idx <= objRef.size() ) {
}
}
...or just elide the auto idx entirely, assuming you have no further use for it:
if( diff * 2 <= objRef.size() ) {
}