Pass and return a char array.

[vasilenko93]

I am passing and returning a char array wrong. How do I make a function that takes in a char array, does something to it, and returns it.

Here is the code I have now, any way to make this function work?

#include <iostream>

using namespace std;

char[] Xout(char[], int);

int main(int argc, char* argv[])
{
    const int LEN = 64;
    char message[LEN ];

    cin.getline(message, LEN);
    message = Xout(message, LEN);
    cout << message;

    return 0;
}

char[] Xout(char message[], int length)
{
    for(i = 0; i < length; i++)
    {
        message[i] = 'X';
    }
    return message;
}

Code::Blocks gives this error.

C:\Users\[...]\stringTest\main.cpp|5|error: expected unqualified-id before '[' token|
C:\Users\[...]\stringTest\main.cpp||In function 'int main()':|
C:\Users\[...]\stringTest\main.cpp|13|error: 'Xout' was not declared in this scope|
C:\Users\[...]\stringTest\main.cpp|19|error: expected unqualified-id before '[' token|
||=== Build finished: 3 errors, 0 warnings (0 minutes, 0 seconds) ===|

I think I am passing it correctly, I just don't know how to return it.

Thanks

[MrHutch]

You don't need to return it.

Since an array is essentially a pointer, any operations performed in the function will affect the array you pass in.

[Cubbi]

It appears that you're trying to use arrays of char to represent strings. Why not just use strings?

#include <iostream>
#include <string>

std::string Xout(const std::string& message)
{
    return std::string(message.size(), 'X');
}

int main()
{
    std::string message;
    getline(std::cin, message);
    message = Xout(message);
    std::cout << message << '\n';
}

[vasilenko93]

@Cubbi, I am not using string because I am experimenting with char arrays.
@iHutch105, that makes sense. But what if I create an array of chars inside a function and need to return it.

Without making anything a "string", can I fix this function?

[Cubbi]

Functions cannot return C-style arrays. They can only modify them by reference or through pointers.

[vasilenko93]

@Cubbi, yeah I made it a void and everything worked out. I did not know that you cannot return a char array.

Thanks.

[andywestken]

You are aware that when you use []s (empty or otherwise) for a parameter, it is just another way of writing a pointer? Such that if you try to compile both

void Xout(char message[], int length)
{
}

and

void Xout(char* message, int length)
{
}

the compiler will complain about a redefinition, whereas if they'd been distinct types, they would have been seen as different overloads. (And any value in the []s is just ignored.)

As the [] form acts like a pointer, I always write functions like this using the * form instead, to make this totally clear.

While you cannot return a char[], you can do this (with pointers.)

char* Xout(char* message, int length)
{
    for(i = 0; i < length; i++)
    {
        message[i] = 'X';
    }
    return message;
}

An approach which is used by some C library functions, e.g. strcpy, strcat, ... (i.e. they return a pointer to the buffer you gave them in the first place.)

#include <iostream>
using namespace std;

char* Xout(char* message, int length);

int main()
{
    const int LEN = 64;
    char message[LEN];

    cin.getline(message, LEN);
    cout << Xout(message, LEN) << endl;

    return 0;
}

char* Xout(char* message, int length)
{
    for(int i = 0; i < length; i++)
    {
        message[i] = 'X';
    }
    return message;
}

Andy

PS Strictly speaking

void Xout(char message[], int length);

looks like

void Xout(char * const message, int length);

rather than

void Xout(char* message, int length);

but the const-ness of the pointer isn't enough to make these functions look like different overloads to the compiler.