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.

• Oliver: I would suggest this -> devx.com/tips/Tip/13291
• Dinaiz: 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 ?
• johnsyweb: Do you really ned to copy the array? Why not just use the same array?
• A Petrov: 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.
• Dinaiz: 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

Answer 1

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.

Answer 2

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

Answer 3

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

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

• Benjamin Bannier: Depending on what his arrays contain this can be problematic since it doesn't invoke copy constructors but copies raw memory.
• Oliver: 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: Did you benchmark this? With my compiler and int arrays std::copy is as fast as memcpy but much safer.
• Oliver: 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