How to compare const char* with a string in C++?

Question

I am working with C++ and I am trying to compare strings.

Below is my code which gives me back const char* -

    const char* client_id() const {
        return String(m_clientPos);
    }

And now I am comparing the strings like this -

cout<<client_ptr->client_id()<< endl;
if (strcmp(client_ptr->client_id(), "Hello")) {
    ..
} else {
    ..
}

but it never goes into if statement. But my cout prints out Hello correctly. Is there anything wrong I am doing?

why you converting m_clientIdPos to string if the return type is const char*? — Rakib
– Rakib, Commented May 21, 2014 at 2:43
That's not my code base. Somebody else wrote it like that. Is there any problem with that? — john
– john, Commented May 21, 2014 at 2:44
there is obvious problem, String is not built in type, (did u mean string?). if there is a user defined String type, then the code will not compile — Rakib
– Rakib, Commented May 21, 2014 at 2:45

Community · Accepted Answer · 2020-06-20 09:12:55Z

4

You need to do if (0 == strcmp(...

See http://www.cplusplus.com/reference/cstring/strcmp/

strcmp

Returns an integral value indicating the relationship between the strings: A zero value indicates that both strings are equal. A value greater than zero indicates that the first character that does not match has a greater value in str1 than in str2; And a value less than zero indicates the opposite.

edited Jun 20, 2020 at 9:12

CommunityBot

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answered May 21, 2014 at 2:45

akn

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Comments

Sergey Kalinichenko · Accepted Answer · 2014-05-21 02:45:36Z

2

it never goes into if statement.

The strcmp function returns zero when the strings are the same, so you should see the code hit the else branch when the two strings are equal to each other.

A zero value indicates that both strings are equal.
A value greater than zero indicates that the first character that does not match has a greater value in str1 than in str2;
And a value less than zero indicates the opposite.

Since String does not look like a built-in class and assuming that you have access to its source, you may be better off making the comparison with const char* a member function of the String class.

answered May 21, 2014 at 2:45

Sergey Kalinichenko

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