Determining the correct size for a C++ array

Question

I need to be able to set the size of an array based on the number of bytes in a file.

For example, I want to do this:

// Obtain the file size.
    fseek (fp, 0, SEEK_END);
    size_t file_size = ftell(fp);
    rewind(fp);

// Create the buffer to hold the file contents.
    char buff[file_size];

However, I get a compile time error saying that the size of the buffer has to be a constant.

How can I accomplish this?

Answer 1

Use a vector.

std::vector<char> buff(file_size);

The entire vector is filled with '\0' first, automatically. But the performance "lost" might not be noticable. It's certainly safer and more comfortable. Then access it like a usual array. You may even pass the pointer to the data to legacy C functions

legacy(&buff[0]); // valid!