Thread: A couple of questions

I am learning the STL and have some questions.

Code:

#include <iostream>
#include <vector>
#include <string>
using namespace std;

int main()
{
	vector<string> vec;
	vec.push_back("test");

	string s(vec[0]);	//turn vec[0] into a string named s
	std::string c( s.size(), char() );
	cout << c << endl;
	copy( s.begin(), s.end(), c.begin() );
	cout << c << endl;

	
	return 0;
}

1. In the first cout, why doesn't c print out?
2. If I eliminate std::string and define string c above, this doesn't work. I get an error: no match for call to ‘(std::string) (size_t, char)’. What is it that std::string is doing in this case?

Because at first c contains only characters '\0' which are non-printable.

So is this similar to how C puts '\0' at the end of an array only at the beginning of a string? And why do I need std::string in front of c( s.size(), char() );? If I declare c as a string and remove std::string, I get an error.

Here is the code with the changes as compared to the original in the first post.

Code:

#include <iostream>
#include <vector>
#include <string>
using namespace std;

int main()
{
	vector<string> vec;
	vec.push_back("test");
	string c;//added

	string s(vec[0]);	
	c( s.size(), char() );//deleted std::string
	cout << c << endl;
	copy( s.begin(), s.end(), c.begin() );
	cout << c << endl;

  	
	return 0;
}

Code:

string_copy1.cpp: In function ‘int main()’:
string_copy1.cpp:13: error: no match for call to ‘(std::string) (size_t, char)’

Also, If I change some of the code to the following:

Code:

std::string c( s.size(), char() );
	for(int i = 0; i < c.size(); i++)
		cout << c[i];
	cout << endl << c.size();

I find that, cout << c[i];, produces all spaces yet c.size() prints out the number 4. Is c( s.size(), char() ) an integer? I hope I've explained this well enough. I am really confused on this.

You can only call the constructor when you define the variable. Just like you had

Code:

std::string c( s.size(), char() );

you can have

Code:

string c( s.size(), char() );