C++ pointing to array in another function

Question

I've got Function1 where user inputs data in array1. I must make array2 in Function2 to be equal to array1 from Function1.

How do I "tell it" that it should use array1 from Function1?

I've tried

array2[50] = array1[50];

but of course that is not working.

What is your goal ? Do you only need the values of array1 to be read by Function2 ? do you need to modify them ? Did you consider using something like a vector instead of an array ? — Dinaiz
– Dinaiz, Commented May 7, 2012 at 10:58
Do you really ned to copy the array? Why not just use the same array? — johnsyweb
– johnsyweb, Commented May 7, 2012 at 10:58
I needed to copy the array and modify the copy. I have yet to study how vectors work, so I have no idea how to use them. Thanks though. — A Petrov
– A Petrov, Commented May 7, 2012 at 11:56
Vectors work like "smart arrays". Besides automatic resizing and bounds checking, you can simply do vector2=vector1 and vector2 will be an independant copy of vector 1 — Dinaiz
– Dinaiz, Commented May 8, 2012 at 20:09

Rob Cooper · Accepted Answer · 2012-05-07 10:23:27Z

2

You need to copy array1 elementwise into array2, e.g.

for (unsigned i=0; i<array1_size; ++i) {
    array2[i] = array1[i];
}

You can also use std::copy from the algorithm header.

std::copy(array1, array1 + array1_size, array2);

For both approaches you need to know the number of elements in array1 (array1_size in the examples). Also, array2 needs to be at least as big as array1.

edited May 7, 2012 at 10:23

Rob Cooper

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answered May 7, 2012 at 9:27

Benjamin Bannier

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Comments

besworland · Accepted Answer · 2012-05-07 09:29:30Z

0

Iterate over all elements in one array and assign them to the second one.

answered May 7, 2012 at 9:29

besworland

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Comments

Oliver · Accepted Answer · 2012-05-07 09:34:40Z

-1

memcpy(second_array, first_array, sizeof(second_array));

[Original Source Site][http://www.devx.com/tips/Tip/13291]

answered May 7, 2012 at 9:34

Oliver

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4 Comments

Benjamin Bannier Over a year ago

Depending on what his arrays contain this can be problematic since it doesn't invoke copy constructors but copies raw memory.

Oliver Over a year ago

Well there is no indicator in the question that shows that there are pointers to structures or objects, in addition there is no hint that a shallow or deep copy is needed, if he only has int's or chars in the table the application will me enormously fast compared to std::copy, i claim that more than 90% of all realtime systems use those low level mechanisms to copy arrays and even single objects

Benjamin Bannier Over a year ago

Did you benchmark this? With my compiler and int arrays std::copy is as fast as memcpy but much safer.

Oliver Over a year ago

This can depend on your platform/compiler , std::copy uses memmove which is not as fast as memcpy because it containts extra checks, i have no system here to properly make performance tests, if you make 1000 memcpy's vs 1000 memoves you will already see the difference, adding the std::copy's check will decrease performance again

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