How Can I Efficiently Initialize All Elements of a C Array to a Non-Zero Value?

Understanding Array Initialization in C

The topic of array initialization in C can be confusing, especially when attempting to initialize all elements to a non-zero default value. In this article, we'll address common questions and provide solutions for effective array initialization.

Initial Value Setting

In the given code:

int array[100] = {-1};

The expectation is for all elements to be initialized to -1. However, only the first element is set to -1; the remaining elements are initialized to 0 with some random values. This is because the omitted elements are implicitly set to 0.

To initialize all elements to -1, the correct syntax is:

int array[100] = {-1, -1, -1, ...};

or you can use the std::fill_n function from the header:

std::fill_n(array, 100, -1);

Performance Comparison

The default initialization method (int array[100] = {-1};) and the std::fill_n method both perform array initialization efficiently. While the default initialization may seem quicker, it's important to note that it can be implementation-dependent and not guaranteed to be faster in all cases.

For larger arrays, the std::fill_n method is generally more efficient as it avoids creating temporary variables for each element assignment.

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