A basic Q about calling templated Functions

The declaration be :

Code:

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template<class X,class Y> void foo(X,Y);

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When calling it, which of the following it a good practice ?...

Code:

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foo("bar",1); // no 1
foo<std::string,int>("bar",1);

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Both seems to be working for me....and I've seen some books sticking for the former

...but the documentation(err..I've only looked into the one from cplusplus)...says(implicitly implies!!) that the implicit one works(or should work) for when X==Y

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Since both i and j are of type int , and the compiler can automatically find out that the template parameter can only be int. This implicit method produces exactly the same result:

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// *that follows after an example..so i,j,int are out of scope here..!

Generally, it is considered better to allow the compiler to work out which function to call from the arguments provided (your first form). If you have to specify which instantiation of the function to call, you might as well write separate functions rather than using a template.

Incidentally, in your example foo("bar", 1) is not equivalent to foo<std::string, int>("bar", 1). Different instantiations of foo() are called.

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Different instantiations of foo() are called.

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I was under the impression that "bar" would be cast into a std::string ..seeing the explicit <std::string,int> ..in the 2nd case
Why is a diff instantiation called instead of that..?

Because "bar" is not a std::string, it is a const char*, so the first one doesn't call the same as the <std::string, int> version.

You are under the wrong impression.

A string literal "bar" is not of type std::string. It is a const array of 4 char. Implicit template instantiation finds a type that is an exact match to the supplied argument, without doing an implicit type conversion.

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so the first one doesn't call

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&&

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Implicit template instantiation finds a type that is an exact match to the supplied argument

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That was for the first one...
Why is it wrong to say that the std::string constructor for a c_string would be called when I explicitly say that the <std::string,int> function is to be compiled ?

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Originally Posted by manasij7479

Why is it wrong to say that the std::string constructor for a c_string would be called then I explicitly say that the <std::string,int> function is to be compiled ?

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It is not wrong to say so, because it is correct. And no one has said otherwise.

..ok.. misunderstood an earlier reply...

foo("bar",1); instantiates to foo<const char[4], int>("bar",1);