member fuctions in string.h

[green-fresh]

today when I tried some of member functions which i read about them in a cpp course i found in my c++ compiler (which is visual c++ 6) this error:
error C2228: left of '.length' must have class/struct/union type
when i used this member function:

str_name.length()

instead of strlen() function>
so :is the problem from the old compiler or what!
and what is the different between strlen() & str_name.length()

thank you all :icon_wink:

[jonsca]

You want to include <string> instead of <string.h> to declare it as a std::string which has a length() method (really just an alias for the size() method). strlen() comes in <string.h> (or <cstring> in a compiler that conforms closely to the standard (which VC++ 6 does not)) and is used on null terminated C style strings. How is str_name defined?

That's rather terse but post back for clarification or google for std::string versus C style strings and there should be a ton of hits.

[Andreas5]

It looks like you did not declare a string.

#include <string>
using namespace std;
string str;
str.length()

[green-fresh]

my code is

#include <string.h>
#include <iostream.h>
#include "genlib.h"
int main()
{
string str="Yes, we went to Gates after we left the dorm.";  ";
int a=str.find("we",0)//strat with the begining of the line
int b=str.find("we",a+1)//strat with the a+1 character and so on....
cout<<"first position is :"<<a<<endl;
cout<<"second position is :"<<b<<endl;
int pos;
str.find('m')
if(pos==string::npos)//if he didn't find any match 
cout<<"no m hear!"<<endl;
else
cout<<"there is m hear !"<<endl;
}

please attention that is used genlib.h :instead of std::string

You want to include <string> instead of <string.h> to declare it as a std::string

the course at:link
said :

you’ll need to include genlib.h to make the short name
string visible instead of requiring the cumbersome std::string.

[jonsca]

Yes, but even in that same handout they have you include

#include <iostream>
#include <string>  // != string.h (I'm not sure how this is resolved in pre standard compilers)
#include "genlib.h" //which must be a custom header to go with their course

If you're just starting out and you're not attached to VC++ 6 due to legacy code or needing MFC, grab the VC++ 2010 Express Edition compiler from M$. It's free and is infinitely more standard compliant than v.6.

you’ll need to include genlib.h to make the short name
string visible instead of requiring the cumbersome std::string.

All this means is that the header probably has using namespace std; (or using std::string by itself) so that you don't have to qualify the name (typing std::string instead of typing string, just as you would have to for std::cout, etc) it doesn't have any bearing on anything else.

[green-fresh]

anyway i think my problem solved.... thanks jonsca .so i can say if i used length() with standard library i would not have any problem Right ?

[green-fresh]

thank you everything goes Right:

#include <string>
#include <iostream>
	using namespace std;
void main()
{


string str="we all love peace yes! we do  ";
int a=str.find("we",0);//strat with the begining of the line
int b=str.find("we",a+1);//strat with the a+1 character and so one>>>>>>>>>
cout<<"first position is :"<<a<<endl;
cout<<"second position is :"<<b<<endl;
int pos;
pos=str.find('m');
if(pos==string::npos)
cout<<"no m hear!"<<endl;
else
cout<<"there is m hear !"<<endl;
}

output:
first position is :0
second position is :34
there is m hear !
Press any key to continue

[jonsca]

Classes can have member variables and methods.

class Example //this could just as easily be a struct as both it's members are public
{
    public:
        int exampleint;
        void examplemethod() { //do something }
};

int main()
{
  int num;
  Example ex;
  num.method();  //int is a native type not a class struct or union, can't use the .(it has no methods)
  //the above line would generate a message similar to the one you had, I believe (I didn't compile it and can't remember)
  num = ex.exampleint; //ok we can access exampleint by the .
  ex.examplemethod(); //works as ex is an object of a class
  return 0;
}

However, in your case it is because it is not recognizing the type std::string because your headers are too old (at least that what it seems like).

[jonsca]

Glad it worked!

void main()

You had it right the first time with int main. main returns an int according to the standard.