无法将 'char (*)[200]' 转换为 'char**'

Question

#include <iostream>
#include <string.h>

using namespace std;

void ArrayTimesThree(char*, const char*);

int main()
{
    char s1[200], s2[200], circleword[200];
    cin.getline(s1, 200);
    cin.getline(s2, 200);

    ArrayTimesThree(circleword, s1);
    cout<<circleword[1];
}

void ArrayTimesThree(char *dest[], char *source[])
{
    *dest[0] = NULL;
    strcat(*dest, *source);
    strcat(*dest, *source);
    strcat(*dest, *source);
}

main.cpp|21|error: cannot convert 'char (*)[200]' to 'char**' for argument '1' to 'void ArrayTimesThree(char**, char**)'

Answer 1

You're passing ArrayTimesThree a char*, however, in the method signature you're telling it to expect a char**. Don't forget that that using the [] operator counts as a dereference. Try this:

#include <iostream>
#include <string.h>

using namespace std;

void ArrayTimesThree(char*, char*);

int main()
{
    char s1[200], s2[200], circleword[200];
    cin.getline(s1, 200);
    cin.getline(s2, 200);

    ArrayTimesThree(circleword, s1);
    cout<<circleword[1];

    return 0;
}

void ArrayTimesThree(char *dest, char source[])
{
    dest[0] = '\0';
    strcat(dest, source);
    strcat(dest, source);
    strcat(dest, source);
}

Disclaimer: I'm not sure what exactly you're expecting out of this code, so I cannot guarantee the logic is correct; however, this will take care of your compiler errors and seems to function correctly for how the code is written.

Answer 2

The problem is really just because your initial declaration of ArrayTimesThree (which is the 'correct' one) doesn't match the definition you later give (which is wrong, in fact). Change your definition as below and it works:

void ArrayTimesThree(char* dest, const char* source) // Needs to be the same as in the previous declaration!
{
    dest[0] = '\0';   // Don't assign a string pointer to NULL! Instead, set its first character to the nul character
//  strcpy(dest, ""); // ALternatively, use strcpy with an empty string to clear "dest"
    strcat(dest, source); // strcat takes char* and const char* arguments ...
    strcat(dest, source); // ... so there is no need to 'deference the values ...
    strcat(dest, source); // ... now that the argument types have been 'corrected'
}

Incidentally, I notice that the input value for s2 in your main function is never actually used … is this what you intend, for now?