copy one string into another

[umair37]

how to copy one string into another using LOOPS.(i am talking about default string class)??
the code given below does not work.
please teach me
void function(string str1)
{
string str2;
int i=0;
while(str1[i]!=NULL)
{
str2[i]=str1[i];
i++;
}
}

[LB]

Of course it does not work. str2 has a size of 0.

Why not just do this?

1 2 3 4 5 6

string s1 ("Hello"); string s2 ("Hi"); cout << s1 << " " << s2 << endl; s2 = s1; s1 = "Bye"; cout << s1 << " " << s2 << endl;

Hello Hi Bye Hello

[therockon7throw]

Hi

string str2 = "" ; and than either use push_back or += operator, when you have to copy the source string using a loop

[LB]

It is more efficient to either use operator= or to resize string 2 beforehand.

[therockon7throw]

It is not, it is very simple

string s1 = "hallo I am Here";
string s2;
string s3;
for(int i = 0 ; i < s1.size() ; i++)
	s2.push_back(s1[i]), s3 += s1[i];

cout<<s1<<endl<<s2<<endl<<s3<<endl;

[umair37]

thanks to you man.it works

[vlad from moscow]

There is no such an entity as "default string class" in C++.
There are character arrays and template class std::string in C++.
I think that you meant character arrays. Then your function will look

char * CopyString( char *dest, const char *source )
{
   char *p = dest;

// the comparision is used that avoid compiler warning
// otherwise you can write simply while ( *p++ = *source++ );
   while ( ( *p++ = *source++ ) != '\0' ); 

   return ( dest );
}

If template class std:;string is used then it is better to assign one string to another withou writing any function

std::string source( "Hello" );
std::string dest;

dest = source;

[LB]

LB wrote:

It is more efficient to either use operator= or to resize string 2 beforehand.

therockon7throw wrote:

It is not, it is very simple

string s1 = "hallo I am Here";
string s2;
string s3;
for(int i = 0 ; i < s1.size() ; i++)
	s2.push_back(s1[i]), s3 += s1[i];

cout<<s1<<endl<<s2<<endl<<s3<<endl;

It is more efficient to use operator= or to resize the string beforehand.

string s1 ("Hello, I am here."), s2, s3;
s2.reserve(s1.length());
s3.resize(s1.length(). '\0');
for(string::iterator it = s1.begin(); it != s1.end(); ++it)
{
    s2 += *it; //or s2.append(*it);
}
for(string::size_type i = 0; i < s1.length(); ++i)
{
    s3[i] = s1[i];
}

Note that it is both easier and more efficient to use operator= as I originally wrote: http://www.cplusplus.com/forum/general/63898/#msg345641

There is no reason ever to copy a std::string character for character unconditionally.