Parameter mismatch with ?: operator

[Old Wolf]

My compiler rejects this:

std::string foo()
{
std::string s;
return some_condition() ? s : "";
}

saying that the last two operands of ?: must be the same type.
I have to fix it by changing "" to std::string() .

Is this correct behaviour? I remember reading that the compiler
ought to try implicitly converting one of the operands to the
type of the other.

[upashu2]

>std::string foo()
{
std::string s;
return some_condition() ? s : "";
}

My Compiler is not showing any problem : gcc 3.4.2, vc++7.1
saying that the last two operands of ?: must be the same type. Absolutely right. I have to fix it by changing "" to std::string() .

It should be implicit conversion.Most probably your compiler either
don't support it or it has a option for it and that option is turned
off.

[Gabriel]

> My compiler rejects this:

What compiler do you use?

[Torsten Mueller]

"Old Wolf" <ol*****@inspire.net.nz> schrieb:

std::string foo()
{
std::string s;
return some_condition() ? s : "";
}

saying that the last two operands of ?: must be the same type. I
have to fix it by changing "" to std::string() .

Is this correct behaviour? I remember reading that the compiler
ought to try implicitly converting one of the operands to the type
of the other.

I would also suggest to fix this as you describe it yourself.
Otherwise the compiler looks for an implicit constructor matching a
const char* parameter. If your code is compiled with a STL
implementation using explicit constructors the compiler will not use
even a matching constructor.

I find implicit constructors bad style because people beeing not
familiar with this (especially beginners) don't even know that there's
a constructor and from what class. It's the same with function
parameters.

T.M.

[Wolfgang Forstmeier]

In my opinion the compiler is right,
because you had to return an std::string
and "" is not a std::string.

Greetings Wolfgang...
Old Wolf wrote:

My compiler rejects this:

std::string foo()
{
std::string s;
return some_condition() ? s : "";
}

saying that the last two operands of ?: must be the same type.
I have to fix it by changing "" to std::string() .

Is this correct behaviour? I remember reading that the compiler
ought to try implicitly converting one of the operands to the
type of the other.

[Old Wolf]

Gabriel wrote:

My compiler rejects this:

What compiler do you use?

Borland C++Builder 5 (compiler version 5.5.1).
It looks like it's just a compiler bug then -- the library
(Rogue Wave 2.1.1) doesn't use explicit constructors.