C++ 风格和 0 到 size_t(0) 的转换

Question

Is using size_t(0) the same as using 0 in the following code?

const string foo = "testing";
const size_t pos = foo.find("i");
string name = foo.substr(size_t(0), pos);

That is, when I put only 0 is it converted to size_t(0) ? If so, is one form preferred over the other? My guess is that size_t(0) is the best one to use because it makes the conversion explicit. On the other hand, perhaps some programmers consider size_t(0) verbose? I'm guessing in practice no one cares either way.

Answer 1

That is, when I put only 0 is it converted to size_t(0)?

The conversion is implicit since substr is:

basic_string substr( size_type pos = 0,
                     size_type count = npos );

Thus your cast is superfluous.

Answer 2

You are type casting the 0 to the same argument type, its a very good practice but not necessary cause this will be converted implicitly.

string substr ( size_t pos = 0, size_t n = npos ) const;

Check out this .