Inserting string in another string at specific index c++/Qt

Question

I have a QString (it may does not matter since I convet it to std::string anyway) which contains the full unix path to a file. e.g. /home/user/folder/name.of.another_file.txt.

I want to append another string to this file name right before the extension name. e.g. I pass to the function "positive", here I call it vector_name and at the end I want to get /home/user/folder/name.of.another_file_positive.txt (note that the last underscore should be added by the function itself.

Here is my code but it does not compile, unfortunately!!

QString temp(mPath); //copy value of the member variable so it doesnt change???

std::string fullPath = temp.toStdString();
std::size_t lastIndex = std::string::find_last_of(fullPath, ".");
std::string::insert(lastIndex, fullPath.append("_" + vector_name.toStdString()));

std::cout << fullPath;

I get the following errors:

error: cannot call member function 'std::basic_string<_CharT, _Traits, _Alloc>::size_type std::basic_string<_CharT, _Traits, _Alloc>::find_last_of(const std::basic_string<_CharT, _Traits, _Alloc>&, std::basic_string<_CharT, _Traits, _Alloc>::size_type) const [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; std::basic_string<_CharT, _Traits, _Alloc>::size_type = long unsigned int]' without object
         std::size_t lastIndex = std::string::find_last_of(fullPath, ".");

cannot call member function 'std::basic_string<_CharT, _Traits, _Alloc>& std::basic_string<_CharT, _Traits, _Alloc>::insert(std::basic_string<_CharT, _Traits, _Alloc>::size_type, const std::basic_string<_CharT, _Traits, _Alloc>&) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; std::basic_string<_CharT, _Traits, _Alloc>::size_type = long unsigned int]' without object
     std::string::insert(lastIndex, fullPath.append("_" + vector_name.toStdString()));

P.S. I would really appriciate if you also can tell me how can I achieve this using QString or Qt library itself!

How about `std::size_t lastIndex = full_path.find_last_of(".");`? It's a member function not a static function. Same goes for `insert`. — Paul Rooney, Jan 06 '16 at 01:30
QString also has [lastIndexOf](http://doc.qt.io/qt-5/qstring.html#lastIndexOf-1), [append](http://doc.qt.io/qt-5/qstring.html#append) and [insert](http://doc.qt.io/qt-5/qstring.html#insert). — Ripple, Jan 06 '16 at 01:43

score 2 · Accepted Answer · answered Jan 06 '16 at 01:34

The reason for the error is that find_last_of and insert are member functions of std::string, not static or non-member functions. Therefore you need an object to access the function.

The corrections are below:

std::size_t lastIndex = fullPath.find_last_of(".");
fullPath.insert(lastIndex, "_" + vector_name.toStdString());
cout << fullPath;

Live Example using dummy data

Also, you may want to test the return values of those function calls. What if there is no "." in the file name?

Inserting string in another string at specific index c++/Qt

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