Swap arrays by using pointers in C++

c++ arrays pointers swap
thornate picture thornate · Aug 3, 2010 · Viewed 35.3k times · Source

I have two arrays of pointers to doubles that I need to swap. Rather than just copy the data within the arrays, it would be more efficient just to swap the pointers to the arrays. I was always under the impression that array names were essentially just pointers, but the following code receives a compiler error:

double left[] = {1,2,3};
double right[] = {9,8,7};

double * swap = left;
left = right; // Error "ISO C++ forbids assignment of arrays"
right = swap; // Error "incompatible types in assignment of `double*' to `double[((unsigned int)((int)numParameters))]'"

Creating the arrays dynamically would solve the problem, but can't be done in my application. How do I make this work?

Answer

Daniel picture Daniel · Aug 3, 2010 
double array_one[] = {1,2,3};
double array_two[] = {9,8,7};

double *left = array_one;
double *right = array_two;

double * swap = left;
left = right;
right = swap;

Works nicely.

edit: The definitions array_one and array_two shouldn't be used and the doubleleft and doubleright should be as public as your original left and right definitions.

Related questions

Return array in a function

I have an array int arr[5] that is passed to a function fillarr(int arr[]): int fillarr(int arr[]) { for(...); return arr; } How can I return that array? How will I use it, say I returned a pointer how am …

Read More
Passing a 2D array to a C++ function

I have a function which I want to take, as a parameter, a 2D array of variable size. So far I have this: void myFunction(double** myArray){ myArray[x][y] = 5; etc... } And I have declared an array elsewhere in my …

Read More
How to get the real and total length of char * (char array)?

For a char [], I can easily get its length by: char a[] = "aaaaa"; int length = sizeof(a)/sizeof(char); // length=6 However, I cannot do like this to get the length of a char * by: char *a = new char[10]; int length = …

Read More