How to convert std::string to lower case?

Question

I want to convert a std::string to lowercase. I am aware of the function tolower(), however in the past I have had issues with this function and it

Answer 1

Copy because it was disallowed to improve answer. Thanks SO

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string test = "Hello World";
for(auto& c : test)
{
   c = tolower(c);
}

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Explanation:

for(auto& c : test) is a range-based for loop of the kind
for (range_declaration:range_expression)loop_statement:

1. range_declaration: auto& c
   Here the auto specifier is used for for automatic type deduction. So the type gets deducted from the variables initializer.

2. range_expression: test
   The range in this case are the characters of string test.

The characters of the string test are available as a reference inside the for loop through identifier c.