I'm failing fully valid code in the _begin and _end pointers

Problem.

The problem is that _beginand _endare not advisable names to use in variables.

Names beginning with an underscore ( _), while not being keywords in the C++ language, are reserved for use by compilers, so using them can interfere with their operation.

What happened?.

For example, the compiler gcc(used in the failing code) declares the symbols _etext, _edataand_end (my translation):

DESCRIPCIÓN
       La dirección de estos símbolos indica el final de varios segmentos
       del programa:

       etext  Esta es la primera dirección tras el final del segmento de
              texto (el código del programa).

       edata  Esta es la primera dirección pasado el final del segmento
              datos inicializados.

       end    Esta es la primera dirección pasado el final del segmento
              de datos no inicializados (también conocido como segmento
              BSS).

NOTAS
       En algunos sistemas los nombres de estos símbolos son precedidos
       por guiones bajos, esto es: _etext, _edata y _end. Estos símbolos
       también son definidos por programas compilados en Linux.

_endSurely the compiler prompt has hidden the variable _endand an attempt has been made to modify a memory address that we should not have access to, giving rise to the segmentation fault.

Technical details.

The C++ standard states that compilers can use variables beginning with an underscore ( _) at their convenience:

In the section §2.10(translation and highlighting are mine):

2.10 Identifiers

...

3. Additionally, some identifiers are reserved for C++ implementations and should not be used for other purposes; no diagnosis is required .

   3.1. — Each identifier that contains a double underscore __or begins with an underscore followed by an uppercase letter is reserved for whatever use the implementation requires .

   3.2. — Each identifier beginning with an underscore is reserved for use by the implementation as a name in the global namespace .

The standard itself indicates that no diagnosis is required in case an identifier considered as reserved is used in the code. This means that unlike keywords that raise a compiler error if used as identifiers, reserved identifiers do not raise a compiler error or alarm when used in code.

Solution.

Do not use the underscore ( _) to name variables or macros:

#include <iostream>

constexpr std::size_t BUFF_SIZE { 256u };

int buffer[BUFF_SIZE] {};
int *begin = buffer;
int *end   = buffer + (BUFF_SIZE / 2u);

int main()
{
    for (unsigned indice{}; indice < (BUFF_SIZE / 2u); ++indice) {
        *(begin + indice) = indice;
        *(end + indice)   = (BUFF_SIZE / 2u) - indice;
    }

    for (const auto &v : buffer) std::cout << v << '\n';

    return 0;
}

The above code prints:

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