Replace a string from a vector of string C++

Question

I have a vector of string constructed using:

vector<string> names;
names.push_back("Gates");
names.push_back("Jones");
names.push_back("Smith");
names.push_back("Gates");

I want to replace "Gates" with "Bill", for every occurrence of "Gates". For this the easiest solution I know is to use the replace function from algorithm and use it as:

replace(names.begin(), names.end(), "Gates", "Bill");

But I am getting following error:

 parameter type mismatch:incompatible types 'const char (&)[6]' and 'const char[5]'.

I can solve it using implicit type casting like this:

replace(names.begin(), names.end(), "Gates", (const char (&)[6]) "Bill");

Can anyone explain what this error is, and better way to solve it or better way to do it. Or why do we need this type casting.

In C++17 you can do replace(names.begin(), names.end(), "Gates"s, "Bill"s) which looks a lot better. — David G
– David G, Commented Jun 20, 2017 at 23:02

Weak to Enuma Elish · Accepted Answer · 2017-06-17 04:22:37Z

5

The old/new value parameters in std::replace share the same type.

For example, the function might look like:

template<class ForwardIt, class T>
void replace(ForwardIt first, ForwardIt last, const T& old_value, const T& new_value);

Stolen from here, not that it's that significant.

"gates" is a const char[6] but bill is a const char[5], which is why you get the error about being unable to convert it.

You could either wrap each string literal in std::string() or just use the unary + operator to decay each literal to a const char*.

replace(names.begin(), names.end(), +"Gates", +"Bill"); //shorter
replace(names.begin(), names.end(), std::string("Gates"), std::string("Bill")); //clearer

I'm pretty sure ((const char (&)[6]) "Bill") violates strict aliasing, so I'd avoid casting between array types like that.

answered Jun 17, 2017 at 4:22

Weak to Enuma Elish

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Basile Starynkevitch · Accepted Answer · 2017-06-17 04:20:36Z

2

I would suggest (assuming some using std;)

 replace(names.begin(), names.end(), string{"Gates"}, string{"Bill"});

since the type of "Gates" is char[6] (decayed to char*) and you want to replace std::string-s (not char* !!).

answered Jun 17, 2017 at 4:20

Basile Starynkevitch

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