strlen() function problem in C++

sajith · 09-28-2005, 07:11 AM

hai sir

i have problem when using the strlen() function in C++

the code of that is

#include <iostream>
#include <cstring>
using namespace std;

int main() {
char str1 = 'b';
string str2 = "foo";
string str3;
int l=strlen(str2); //error
cout<<l<<"\n";
str3 = str2 + str1;
cout << str3 << endl;
return 0;
}

error i got is

:9: error: cannot convert ‘std::string’ to ‘const char*’ for argument ‘1’ to ‘size_t strlen(const char*)’

please tell me solution

sind · 09-28-2005, 07:53 AM

It looks like jtshaw has answered your question here. jtshaw's comments about strcat() apply to strlen() as well.

The length() member function of std::string will do what you're after.

~sind

jtshaw · 09-28-2005, 08:20 AM

Here is a list of things the STL String (aka C++ String) class contains.

stephen9 · 01-14-2006, 06:34 AM

hey guys can anyone help me how to use string.h to create a singular/plural program, is a project of mine and i need it to get A+ on it erm can anybody help me?????

spooon · 01-14-2006, 03:48 PM

Quote:

Originally Posted by stephen9

hey guys can anyone help me how to use string.h to create a singular/plural program, is a project of mine and i need it to get A+ on it erm can anybody help me?????

This is unrelated to this thread; start a new thread. Also, we don't help people with homework.

dmail · 01-14-2006, 03:53 PM

Quote:

Originally Posted by spooon

... Also, we don't help people with homework.

Why do people say this?
The rules say

Quote:

Do not expect LQ members to do your homework - you will learn much more by doing it yourself.

There is helping someone and then theres doing the work. These two are completely different. Post your question stephen9 and I will try and help.

kike_coello · 01-16-2006, 10:21 AM

#include <iostream>
#include <cstring>
using namespace std;

int main() {
char str1 = 'b';
string str2 = "foo";
string str3;
//int l=strlen(str2); //error
int l=strlen("str2");
cout<<l<<"\n";
str3 = str2 + str1;
cout << str3 << endl;
system("pause");
return 0;
}

spooon · 01-16-2006, 02:53 PM

Quote:

Originally Posted by kike_coello

//int l=strlen(str2); //error
int l=strlen("str2");

No, this is very wrong. You are taking the length of the literal string "str2", which is always 4; and you are not doing anything with the variable str2 itself, which is the intended action. Correct way would be

Code:

int l = str2.length();

kike_coello · 01-16-2006, 08:44 PM

hey dude, how is it wrong, when it worked, i ran that code on xp.

jtshaw · 01-16-2006, 09:14 PM

As typed "int l=strlen("str2");" takes the length of the string "str2" not the string held in the variable str2. str2.length() is correct.

Here is an example and it's output:

Code:

#include <iostream>
#include <cstring>
using namespace std;

int main()
{
        string str2="foo";
        int len1 = str2.length();
        int len2 = strlen("str2");
        int len3 = strlen(str2.c_str());

        cout << "str2.length() = " << str2.length() << endl
             << "strlen(\"str2\") = " << strlen("str2") << endl
             << "strlen(str2.c_str()) = " << strlen(str2.c_str()) << endl;
}

Code:

johnshaw@Quaqmire-OSX ~ $ ./test2 
str2.length() = 3 
strlen("str2") = 4
strlen(str2.c_str()) = 3

I can not think of any situation where you want to put a variable in quotes in the C++ language. If you want to use the strlen function (which is a C function) you need to use the .c_str() method on your stl string.