Question on std::string

Hello all, hopefully a quick question for you guys.

I'm trying to take a std::string object and be able to assign individual elements in it with arbitrary characters. Meaning, I want to be able to do something like:

Code:

string pString;
for (int x = 0; x < 10; x++)
{
       pString[x] = x;
}

How can I allocate memory to my std::string object without assigning specific values to it? Is it possible to do something like this?

Code:

string pString(10);

Will that assign enough memory for 10 characters? (9 plus null terminator I mean).

Will that assign enough memory for 10 characters? (9 plus null terminator I mean).

Wow! How long would that take to test? 30 seconds? 1 full minute if you type slow?

http://www.cppreference.com/cppstring/

One nice thing about std::string is that you don't need to worry about the null terminator.

In your example you can use push_back()

Code:

#include <iostream>
#include <string>

int main()
{
        std::string str;
        for(char i='0'; i <= '9'; i++)
                str.push_back( i );
        std::cout<<str<<std::endl;
}

That's not really the answer I'm looking for. I want to be able to assign memory for use later, I don't want to have to use some function to fill a std::string with data already processed. I want to do the std::string equivalent of:

Code:

char* s = new char[10];

But I don't want to have to create a pointer to a std::string.

I want to do the std::string equivalent of:

char* s = new char[10];

Why?

Gah, nevermind, I solved my problem using stringstream.

How can I allocate memory to my std::string object without assigning specific values to it? Is it possible to do something like this?

Code:

string pString(10);



Will that assign enough memory for 10 characters? (9 plus null terminator I mean).

That is exactly what you would do. Also, most implementations (i know SGI's does) of std::string reserve an extra byte when realloc'ing for the null terminator should the c_str() member function be called. For example, if you append a 9 character string to the end of a std::string with 9 reserved characters, the implementation would likely still call realloc() because it doesn't have the additional byte for the null terminator allocated.

How can I allocate memory to my std::string object without assigning specific values to it? Is it possible to do something like this?

string pString(10);

Will that assign enough memory for 10 characters? (9 plus null terminator I mean).

That is exactly what you would do.

Really? When looking at the constructors for the std:string class, I didn't see any that took an int argument. In addition, my compiler gave me this error when I tested it:

C:\Beginning C++\test2\main.cpp(14) : error C2664: '__thiscall std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >::std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >(const class std::allo
cator<char> &)' : cannot convert parameter 1 from 'const int' to 'const class std::allocator<char> &'
Reason: cannot convert from 'const int' to 'const class std::allocator<char>'
No constructor could take the source type, or constructor overload resolution was ambiguous

Originally Posted by 7stud

Really? When looking at the constructors for the std:string class, I didn't see any that took an int argument. In addition, my compiler gave me this error when I tested it:

C:\Beginning C++\test2\main.cpp(14) : error C2664: '__thiscall std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >::std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >(const class std::allo
cator<char> &)' : cannot convert parameter 1 from 'const int' to 'const class std::allocator<char> &'
Reason: cannot convert from 'const int' to 'const class std::allocator<char>'
No constructor could take the source type, or constructor overload resolution was ambiguous

Err, my bad, the constructor is actually

Code:

string( size_type length, const char& ch );

http://www.cppreference.com/cppstrin...structors.html
In this case the second argument could be any character.