CODEWITHSUNDEEP
c++
olidev
olidev

Reputation: 20624

modifying length of an array in C++

If I have this float array declaration:

float tables[10];

How can I change the length of the 'tables' array to 20?

Another question related to the array in C++:

I can not declare an array something like this:

int length=10;

float newTables[length]; // error C2133: 'newTables' : unknown size

Thanks in advance.

Upvotes: 3

Views: 352

Answers (4)

Habba
Habba

Reputation: 1199

If you are fine defining the size of array during build-time, you can use #define

#DEFINE ARRAY_SIZE 20
float tables[ARRAY_SIZE];

Or if you need to specify the size of array during runtime, use new

float* newtables;
newtables = new float[20];

Upvotes: 1

aaranda
aaranda

Reputation: 1

You can not change the length of an array dinamically while running program in C++. About the way you want to declare the array I suggest you the following:

const int length=10;
float newTables[length];

I'm not sure if it's what you want. In this case the variable "length" is a constant and can not be changed in execution.

I hope it helps you.

Upvotes: 0

pmr
pmr

Reputation: 59811

Arrays in C++ have a fixed length. If you want to stick with a pure array you need to allocate the memory dynamically using malloc, realloc and free. However, you should prefer a std::vector or std::deque for dynamic memory allocation.

Upvotes: 1

Björn Pollex
Björn Pollex

Reputation: 76778

You cannot change the length of an array. In C++, you should use an std::vector for dynamic arrays:

#include <vector>

int main() {
    std::vector::size_type length = 10;
    std::vector<float> tables(length); // create vector with 10 elements
    tables.resize(20); // resize to 20 elemets
    tables[15] = 12; // set element at index 15 to value 12
    float x = tables[5]; // retrieve value at index 5
}

Upvotes: 14

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