CODEWITHSUNDEEP
c++multidimensional-array
Daniel Sega
Daniel Sega

Reputation: 333

Copy a matrix/2d array to another in c++

I am trying to copy a 2d array into another 2d array, i have these two array created:

#define mapXcor 50
#define mapYcor 50

char secondStage    [mapXcor][mapYcor];
char currentStage   [mapXcor][mapYcor];
//mapXcor and mapYcor are constant integers

Now my secondStage[][] array is populated with values on it, but currentStage[][] isn't, and i want to assign the values of secondStage to currentStage. So i created the function bellow:

void populateArray(char (&arrayA)[mapXcor][mapYcor], char arrayB[mapXcor][mapYcor]) {
    for(int a = 0; a < mapXcor + 1; ++a) {
        for(int b = 0; b < mapYcor + 1; ++b) {
            arrayA[mapXcor][mapYcor] = arrayB[mapXcor][mapYcor];
        }
    }
}

populateArray(currentStage[mapXcor][mapYcor],secondStage[mapXcor][mapYcor]);

But when i use the function it gives me a error :

1 IntelliSense: a reference of type "char (&)[20][50]" (not const-qualified) cannot be initialized with a value of type "char"

2 IntelliSense: argument of type "char" is incompatible with parameter of type "char (*)[50]"

How could I fix this?

Upvotes: 2

Views: 18833

Answers (3)

sg7
sg7

Reputation: 6298

#define ROWS 2
#define COLS 2

void copyArray(char (&arrayA)[ROWS][COLS], const char (&arrayB)[ROWS][COLS] ) {

    memcpy(arrayA, arrayB, sizeof(arrayB));
}

int main(void){

    char arr1  [ROWS][COLS];
    char arr2  [ROWS][COLS];

    // init arr1
    copyArray(arr2, arr1);

    return 0;
}

Upvotes: 0

Roman Nikitchenko
Roman Nikitchenko

Reputation: 13046

Code you probably are trying to reach. Do not show it to teacher :-) - there is too much from practical programming. Just look and then write your own solutions:

#include <string.h>
#include <stdio.h>

#define mapXcor 5
#define mapYcor 5

static char secondStage    [mapXcor][mapYcor];
static char currentStage   [mapXcor][mapYcor];

void populateArray(char (&arrayA)[mapXcor][mapYcor], const char (&arrayB)[mapXcor][mapYcor]) {
/*
    for(int a = 0; a < mapXcor; ++a) {
        for(int b = 0; b < mapYcor; ++b) {
            arrayA[a][b] = arrayB[a][b];
        }
    }
*/
    memcpy(arrayA, arrayB, sizeof(arrayB));
}

int main()
{
    for(int a = 0; a < mapXcor; ++a) {
        for(int b = 0; b < mapYcor; ++b){
            currentStage[a][b] = a*b + 10*a;
        }
    }

    populateArray(secondStage, currentStage);

    for(int a = 0; a < mapXcor; ++a) {
        for(int b = 0; b < mapYcor; ++b){
            printf("%2i ", secondStage[a][b]);
        }
        printf("\n");
    }

    return 0;
}

Comments:

  • You have bad array index limits in cycle. Look for corrected function under comment.
  • You have wrong indexes in assignment in cycle. Again, commented out code.
  • If you passed one array by reference (destination) why not to use constant reference for source?
  • In practice as your areas have the same type (you could even define them as having the same type) nobody copies them by elements. I have used memcpy() but this is only good if memory areas do not overlap (in this case - yes). check man 3 memcpy.
  • Learn harder :-)

Upvotes: 2

Miguel Prz
Miguel Prz

Reputation: 13792

change the assignment sentence in your for-loop:

arrayA[mapXcor][mapYcor] = arrayB[mapXcor][mapYcor];

by

arrayA[a][b] = arrayB[a][b];

Upvotes: 3

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