CODEWITHSUNDEEP
c++arrays
Taylor Huston
Taylor Huston

Reputation: 1140

Append to the end of a Char array in C++

Is there a command that can append one array of char onto another? Something that would theoretically work like this:

//array1 has already been set to "The dog jumps "
//array2 has already been set to "over the log"

append(array2,array1);
cout << array1;

//would output "The dog jumps over the log";

This is a pretty easy function to make I would think, I am just surprised there isn't a built in command for it.

*Edit

I should have been more clear, I didn't mean changing the size of the array. If array1 was set to 50 characters, but was only using 10 of them, you would still have 40 characters to work with. I was thinking an automatic command that would essentially do:

//assuming array1 has 10 characters but was declared with 25 and array2 has 5 characters
int i=10;
int z=0;    
do{
    array1[i] = array2[z];
    ++i;
    ++z;
}while(array[z] != '\0');

I am pretty sure that syntax would work, or something similar.

Upvotes: 13

Views: 150557

Answers (4)

KillianDS
KillianDS

Reputation: 17176

If you are not allowed to use C++'s string class (which is terrible teaching C++ imho), a raw, safe array version would look something like this.

#include <cstring>
#include <iostream>

int main()
{
    char array1[] ="The dog jumps ";
    char array2[] = "over the log";
    char * newArray = new char[std::strlen(array1)+std::strlen(array2)+1];
    std::strcpy(newArray,array1);
    std::strcat(newArray,array2);
    std::cout << newArray << std::endl;
    delete [] newArray;
    return 0;
}

This assures you have enough space in the array you're doing the concatenation to, without assuming some predefined MAX_SIZE. The only requirement is that your strings are null-terminated, which is usually the case unless you're doing some weird fixed-size string hacking.

Edit, a safe version with the "enough buffer space" assumption:

#include <cstring>
#include <iostream>

int main()
{
    const unsigned BUFFER_SIZE = 50;
    char array1[BUFFER_SIZE];
    std::strncpy(array1, "The dog jumps ", BUFFER_SIZE-1); //-1 for null-termination
    char array2[] = "over the log";
    std::strncat(array1,array2,BUFFER_SIZE-strlen(array1)-1); //-1 for null-termination
    std::cout << array1 << std::endl;
    return 0;
}

Upvotes: 19

masoud
masoud

Reputation: 56479

You should have enough space for array1 array and use something like strcat to contact array1 to array2:

char array1[BIG_ENOUGH];
char array2[X];
/* ......             */
/* check array bounds */
/* ......             */

strcat(array1, array2);

Upvotes: 2

Alok Save
Alok Save

Reputation: 206518

If your arrays are character arrays(which seems to be the case), You need a strcat().
Your destination array should have enough space to accommodate the appended data though.

In C++, You are much better off using std::string and then you can use std::string::append()

Upvotes: 5

Luchian Grigore
Luchian Grigore

Reputation: 258568

There's no built-in command for that because it's illegal. You can't modify the size of an array once declared.

What you're looking for is either std::vector to simulate a dynamic array, or better yet a std::string.

std::string first ("The dog jumps ");
std::string second ("over the log");
std::cout << first + second << std::endl;

Upvotes: 1

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