What type is used in C++ to define an array size?

Question

Compiling some test code in avr-gcc for an 8-bit micro-controller, the line

const uint32_t N = 65537;
uint8_t values[N]; 

I got the following compilation warning (by default should be an error, really)

warning: conversion from 'long unsigned int' to 'unsigned int' changes value from '65537' to '1' [-Woverflow]
uint8_t values[N];

Note that when compiling for this target, sizeof(int) is 2.

So it seems that, at an array size cannot exceed the size of an unsigned int.

Am I correct? Is this GCC-specific or is it part of some C or C++ standard?

Before somebody remarks that an 8-bit microcontroller generally does not have enough memory for an array so large, let me just anticipate saying that this is beside the point.

Answer 1

size_t is considered as the type to use, despite not being formally ratified by either the C or C++ standards.

The rationale for this is that the sizeof(values) will be that type (that is mandatated by the C and C++ standards), and the number of elements will be necessarily not greater than this since sizeof for an object is at least 1.

Answer 2

So it seems that, at an array size cannot exceed the size of an unsigned int.

That seems to be the case in your particular C[++] implementation.

Am I correct? Is this gcc-specific or is it part of some C or C++ standard?

It is not a characteristic of GCC in general, nor is it specified by either the C or C++ standard. It is a characteristic of your particular implementation: a version of GCC for your specific computing platform.

The C standard requires the expression designating the number of elements of an array to have an integer type, but it does not specify a particular one. I do think it's strange that your GCC seems to claim it's giving you an array with a different number of elements than you specified. I don't think that conforms to the standard, and I don't think it makes much sense as an extension. I would prefer to see it reject the code instead.