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std::basic_string::insert

basic_string& insert( size_type index, size_type count, CharT ch );
 (1) 
basic_string& insert( size_type index, const CharT* s );
 (2) 
basic_string& insert( size_type index, const CharT* s, size_type count );
 (3) 
basic_string& insert( size_type index, const basic_string& str );
 (4)
(5) 
basic_string& insert( size_type index, const basic_string& str,
                      size_type index_str, size_type count );
 (until C++14) 
basic_string& insert( size_type index, const basic_string& str,
                      size_type index_str, size_type count = npos);
 (since C++14)
(6) 
iterator insert( iterator pos, CharT ch );
 (until C++11) 
iterator insert( const_iterator pos, CharT ch );
 (since C++11)
(7) 
void insert( iterator pos, size_type count, CharT ch );
 (until C++11) 
iterator insert( const_iterator pos, size_type count, CharT ch );
 (since C++11)
(8) 
template< class InputIt >
void insert( iterator pos, InputIt first, InputIt last );
 (until C++11) 
template< class InputIt >
iterator insert( const_iterator pos, InputIt first, InputIt last );
 (since C++11) 
iterator insert( const_iterator pos, std::initializer_list<CharT> ilist );
 (9) (since C++11) 
basic_string& insert( size_type pos, basic_string_view<CharT, Traits> sv );
 (10) (since C++17) 
template < class T >
basic_string& insert( size_type index, const T& t,
                      size_type index_str, size_type count = npos);
 (11) (since C++17)

Inserts characters into the string.

1) Inserts count copies of character ch at the position index
2) Inserts null-terminated character string pointed to by s at the position index. The length of the string is determined by the first null character (effectively calls Traits::length(s).
3) Inserts the first count characters from the character string pointed to by s at the position index. s can contain null characters.
4) Inserts string str at the position index
5) Inserts a string, obtained by str.substr(index_str, count) at the position index
6) Inserts character ch before the character pointed by pos
7) Inserts count copies of character ch before the element pointed by pos
8) Inserts characters from the range [first, last) before the element pointed by pos. This overload does not participate in overload resolution if InputIt does not satisfy InputIterator. (since C++11)
9) Inserts elements from initializer list ilist before the element pointed by pos
10) Inserts the elements from the string view sv before the element pointed by pos, as if by insert(pos, sv.data(), sv.size())
11) Converts t to a string view sv as if by std::basic_string_view<CharT, Traits> sv = t;, then inserts, before the element pointed by pos, the characters from the subview [index_str, index_str+count) of sv. If the requested subview lasts past the end of sv, or if count == npos, the resulting subview is [index_str, sv.size()). If index_str > sv.size(), or if index > size(), std::out_of_range is thrown. This overload only participates in overload resolution if std::is_convertible_v<const T&, std::basic_string_view<CharT, Traits>> is true and std::is_convertible_v<const T&, const CharT*> is false.

Parameters

index - position at which the content will be inserted
pos - iterator before which the characters will be inserted
ch - character to insert
count - number of characters to insert
s - pointer to the character string to insert
str - string to insert
first, last - range defining characters to insert
index_str - position of the first character in the string str to insert
ilist - std::initializer_list to insert the characters from
sv - std::basic_string_view to insert the characters from
t - object (convertible to std::basic_string_view) to insert the characters from
Type requirements
-InputIt must meet the requirements of InputIterator.

Return value

1-5,10-11) *this
6-9) An iterator which refers to the copy of the first inserted character or pos if no characters were inserted (count==0 or first==last or ilist.size()==0)

Exceptions

1) std::out_of_range if index > size() and std::length_error if size() + count > max_size().
2) std::out_of_range if index > size() and std::length_error if size() + Traits::length(s) > max_size().
3) std::out_of_range if index > size() and std::length_error if size() + count > max_size().
4) std::out_of_range if index > size() and std::length_error if size() + str.size() > max_size().
5) Throws exceptions on the following conditions:
a) std::out_of_range if index > size().
b) std::out_of_range if index_str > str.size().
c) std::length_error if size() + ins_count > max_size() where ins_count is the number of characters that will be inserted.
6-9) (none)
10) std::out_of_range if index > size() and std::length_error if size() + sv.size() > max_size().
11) Throws exceptions on the following conditions:
a) std::out_of_range if index > size().
b) std::out_of_range if index_str > sv.size().
c) std::length_error if size() + ins_count > max_size() where ins_count is the number of characters that will be inserted.
In any case, if an exception is thrown for any reason, this function has no effect (strong exception guarantee). (since C++11)

Example

#include <cassert>
#include <iterator>
#include <string>
using namespace std::string_literals;
int main()
{
    std::string s = "xmplr";
 
    // insert(size_type index, size_type count, char ch)
    s.insert(0, 1, 'E');
    assert("Exmplr" == s);
 
    // insert(size_type index, const char* s)
    s.insert(2, "e");
    assert("Exemplr" == s);
 
    // insert(size_type index, string const& str)
    s.insert(6, "a"s);
    assert("Exemplar" == s);
 
    // insert(size_type index, string const& str,
    //     size_type index_str, size_type count)
    s.insert(8, " is an example string."s, 0, 14);
    assert("Exemplar is an example" == s);
 
    // insert(const_iterator pos, char ch)
    s.insert(s.cbegin() + s.find_first_of('n') + 1, ':');
    assert("Exemplar is an: example" == s);
 
    // insert(const_iterator pos, size_type count, char ch)
    s.insert(s.cbegin() + s.find_first_of(':') + 1, 2, '=');
    assert("Exemplar is an:== example" == s);
 
    // insert(const_iterator pos, InputIt first, InputIt last)
    {
        std::string seq = " string";
        s.insert(s.begin() + s.find_last_of('e') + 1,
            std::begin(seq), std::end(seq));
        assert("Exemplar is an:== example string" == s);
    }
 
    // insert(const_iterator pos, std::initializer_list<char>)
    s.insert(s.cbegin() + s.find_first_of('g') + 1, { '.' });
    assert("Exemplar is an:== example string." == s);
}

See also

appends characters to the end
(public member function)
appends a character to the end
(public member function)

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