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c++classconstructorchararguments
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Reputation: 11

(C++) string literal doesn't match argument list

I'm following along with a C++ book titled "Starting Out with C++: From Control Structures Through Objects" by Tony Gaddis.

There's a programming example that I get an error on. The program creates a constructor for a class which takes two arguments. The two arguments are pointers to chars. Here's part of the class:

class ContactInfo
{
private:
    char *name;
    char *phone;
public:
    ContactInfo(char *n, char *p)
    {
        name = new char[strlen(n) + 1];
        phone = new char[strlen(p) + 1];
        strcpy(name, n);
        strcpy(phone, p);
    }
}

When an object of the ContactInfo class is created, the program passes these values to the constructor.

ContactInfo entry("Kristen Lee", "555-2021");

This all seems to make sense to me, but I get an error when passing "Kristen Lee" to the constructor. The error says:

"no instance of constructor "ContactInfo::ContactInfo" matches the argument list. Argument types are: (const char[12], const char[9])"

I don't understand why this error shows up. The only thing I can think of is that we're trying to pass a value into a variable which holds memory addresses. But, I don't know enough about programming to know if this is the case. I doubt this would be in the textbook if it didn't work at all. Maybe it's a visual studio problem (the IDE I'm using)? I'd really appreciate any help I can get with this problem.

Upvotes: 1

Views: 914

Answers (2)

R Sahu
R Sahu

Reputation: 206737

A string literal can decay to a char const*, not a char*. Hence, you should change your constructor to use char const*.

ContactInfo(char const* n, char const* p) { ... }

As a general principle, unless you want a function to modify its argument, make it const. That's always a better choice. It allows the function to be used using a const object and a non-const object. This applies to passing pointers as well as references to objects.

Upvotes: 0

Tas
Tas

Reputation: 7111

A string literal (e.g. "Kristen Lee") is a const char*: it is unmodifiable by your program. Since the constructor of ContactInfo takes only a char*, the string literal does not match.

This is laid out in the compiler message:

no instance of constructor "ContactInfo::ContactInfo" matches the argument list. Argument types are: (const char[12], const char[9])

Here the compiler is telling you there's no match for the function ContactInfo::ContactInfo and that the arguments you're passing as const char[12] and const char[9].

Your problem can be very easily solved by using std::string instead:

#include <string>
class ContactInfo
{
private:
    std::string name;
    std::string phone;
public:
    ContactInfo(std::string n, std::string p) : name{n}, phone{p}
    {}
};

Notice how much simpler that makes your code, as you no longer need 4 lines of code and to manage your own memory.

Upvotes: 1

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