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c++11castingstatictype-conversion

string length: invalid static_cast

I was expecting this sample code to work:

std::string s;
int number=1;
s = std::to_string(number);
int size=static_cast<int>(s.length);

However it gives the error:

main.cpp:178:39: error: invalid static_cast from type ‘’ to type ‘int’ int size=static_cast(s.length);

Then, I also tried:

int size=atoi(s.length);

Which gives me the error:

 cannot convert ‘std::basic_string<_CharT, _Traits, _Alloc>::length<char, std::char_traits<char> 
... to type ‘const char*’

Then, I tried this option:

int size=atoi(s.c_str());

This one worked. Any hints why atoi(s.length) does not work, and instead atoi(s.c_str()) is required?

So, suppose that I have the input string as 999, the total of digits will be 3. Using s.length would be the best way to get the total of digits, however the s.length casting gives the error.

Solution

  • You did not invoke the length method. You should use int size=static_cast<int>(s.length());: notice the call operator at the end of the length method name.

    However, if by doing this, you are trying to convert the string to an integer, this is wrong. This only gives you the number of characters in the string.