Add elements to a vector during range-based loop c++11

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No you cannot rely on this behaviour. Modifying the vector inside the loop results in undefined behaviour because the iterators used by the loop are invalidated when the vector is modified.

The range based for loop 

for ( range_declaration : range_expression) loop_statement

is essentially equivalent to 

{
    auto && __range = range_expression ; 
    for (auto __begin = std::begin(__range),
        __end = std::end(__range); 
        __begin != __end; ++__begin) { 
            range_declaration = *__begin;
            loop_statement 
    }
}

When you modify the vector, the iterators __begin and __end are no longer valid and the dereferencing __begin results in undefined behaviour.

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