Initializing arrays

[Justin_]

Its been a while since I last coded in c++. I'm wondering what the best way to create an array is if you don't know its size. Must you wait till you know its size or?

I'm basically creating a const unsigned character array to store the hex of a file, incase you wanted to know. So actually another good question to ask would be what is the best function to grab the length of a binary file?

[wtd]

If you don't know the size you'll need? Then don't use an array.

Use one of the STL collections classes.

[Null]

Just expanding what wtd said.

You should try to avoid arrays in C++ in general, as much better solutions exist. The common replacement is the std::vector<Type> containter, which handles its own memory. Here's an example:

code:

#include <iostream> #include <vector> const int SIZE = 10; template <typename T> void display(const std::vector<T> &vec) {         //one way of printing a vector: using indexes         for(int i = 0; i < vec.size(); i++)                 std::cout << vec[i] << std::endl; } int main() {         std::vector<int> numbs;         for(int i = 0; i < SIZE; i++)                 numbs.push_back(i + 1); //append an item         display(numbs); }

[Justin_]

Cool. The only thing is that I'm pretty sure the windows API doesn't work well with these containers.

[md]

you can always do [syntax="cpp"]char *array = new chat[size];/syntax] Just remember to de-allocate the memory with

c++:

delete [] array;

I'm also pretty sure there is a way of getting a normal array out of a vector.

[Justin_]

Thanks.

Quote:

I'm also pretty sure there is a way of getting a normal array out of a vector.

Can anyone confirm this?

[wtd]

Null wrote:

Just expanding what wtd said.

You should try to avoid arrays in C++ in general, as much better solutions exist. The common replacement is the std::vector<Type> containter, which handles its own memory. Here's an example:

code:

#include <iostream> #include <vector> const int SIZE = 10; template <typename T> void display(const std::vector<T> &vec) {         //one way of printing a vector: using indexes         for(int i = 0; i < vec.size(); i++)                 std::cout << vec[i] << std::endl; } int main() {         std::vector<int> numbs;         for(int i = 0; i < SIZE; i++)                 numbs.push_back(i + 1); //append an item         display(numbs); }

In your code, though, since you do know the size of the vector, you would be best off passing that value to its constructor. That will preallocate that much memory, and avoid unnecessary reallocations.

code:

#include <iostream> #include <vector> #include <algorithm> #include <iterator> const int SIZE = 10; int main() {         std::vector<int> numbs(SIZE);         for(int i = 0; i < SIZE; i++)                 numbs.push_back(i + 1); //append an item         std::copy(numbs.begin(), numbs.end(),                 std::ostream_iterator<int>(std::cout, "\n")); }

[Justin_]

If you are passing the addr of an array what is the syntax?

I've got

c++:

function(unsigned char& array); //preprocessor unsigned char array[]; function(array);

[wtd]

Arrays are just glorified pointers. Understand that, and all will become clear.

[Justin_]

I thought I did. Here is what I think it should be:

c++:

function (unsigned char* array); //preprocessor unsigned char array[]; function(array);

Doesn't work though.

[wtd]

Perhaps if you showed the exact code you're using.

[Justin_]

When I try to post it I get a "service temporarily unavailable" message.

So are you saying the above way is the correct way but exterior factors in the code could be impeding?

[wtd]

I'm saying that I find your psuedocode harder to understand than actual code would be.

[Justin_]

Well the data base must be filling up or something... It won't post.

So here I'll give you some more.

c++:

//headers are good give_me_the_array(unsigned char* array);  //preprocessor. int main() {    unsigned char array[];    give_me_the_array(array);    return 0; } void give_me_the_array(unsigned char* array) {    //do something to array }

[wtd]

Why are you not providing a size for the array in its declaration.

If you wish to declare an array thusly, you should:

code:

int *foo; // yada yada foo = new int[some_integer];