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std::string substr() method

// Const version only
constexpr basic_string substr( size_type pos = 0, size_type count = npos ) const;

Returns a substring [ pos, pos + count ).
If the requested substring extends past the end of the string, i.e. count is greater than size() - pos (e.g. if count == npos), the returned substring is [ pos, size() ).

Parameters

  • pos - position of the first character to include
  • count - length of the substring

Return value

String containing the substring [ pos, pos + count ) or [ pos, size() ).

Complexity

Linear in count - O(count).

Exceptions

Throws std::out_of_range if pos > size().

Notes

The returned string is constructed as if by basic_string(data() + pos, count), which implies that the returned string's allocator will be default-constructed — the new allocator might not be a copy of get_allocator().

Example

#include <string>
#include <iostream>

int main()
{
std::string a = "0123456789abcdefghij";

// count is npos, returns [pos, size())
std::string sub1 = a.substr(10);
std::cout << sub1 << '\n';

// both pos and pos+count are within bounds, returns [pos, pos+count)
std::string sub2 = a.substr(5, 3);
std::cout << sub2 << '\n';

// pos is within bounds, pos+count is not, returns [pos, size())
std::string sub4 = a.substr(a.size()-3, 50);
// this is effectively equivalent to
// std::string sub4 = a.substr(17, 3);
// since a.size() == 20, pos == a.size()-3 == 17, and a.size()-pos == 3

std::cout << sub4 << '\n';

try {
// pos is out of bounds, throws
std::string sub5 = a.substr(a.size()+3, 50);
std::cout << sub5 << '\n';
} catch(const std::out_of_range& e) {
std::cout << "pos exceeds string size\n";
}
}
Output
abcdefghij
567
hij
pos exceeds string size
This article originates from this CppReference page. It was likely altered for improvements or editors' preference. Click "Edit this page" to see all changes made to this document.
Hover to see the original license.

std::string substr() method

// Const version only
constexpr basic_string substr( size_type pos = 0, size_type count = npos ) const;

Returns a substring [ pos, pos + count ).
If the requested substring extends past the end of the string, i.e. count is greater than size() - pos (e.g. if count == npos), the returned substring is [ pos, size() ).

Parameters

  • pos - position of the first character to include
  • count - length of the substring

Return value

String containing the substring [ pos, pos + count ) or [ pos, size() ).

Complexity

Linear in count - O(count).

Exceptions

Throws std::out_of_range if pos > size().

Notes

The returned string is constructed as if by basic_string(data() + pos, count), which implies that the returned string's allocator will be default-constructed — the new allocator might not be a copy of get_allocator().

Example

#include <string>
#include <iostream>

int main()
{
std::string a = "0123456789abcdefghij";

// count is npos, returns [pos, size())
std::string sub1 = a.substr(10);
std::cout << sub1 << '\n';

// both pos and pos+count are within bounds, returns [pos, pos+count)
std::string sub2 = a.substr(5, 3);
std::cout << sub2 << '\n';

// pos is within bounds, pos+count is not, returns [pos, size())
std::string sub4 = a.substr(a.size()-3, 50);
// this is effectively equivalent to
// std::string sub4 = a.substr(17, 3);
// since a.size() == 20, pos == a.size()-3 == 17, and a.size()-pos == 3

std::cout << sub4 << '\n';

try {
// pos is out of bounds, throws
std::string sub5 = a.substr(a.size()+3, 50);
std::cout << sub5 << '\n';
} catch(const std::out_of_range& e) {
std::cout << "pos exceeds string size\n";
}
}
Output
abcdefghij
567
hij
pos exceeds string size
This article originates from this CppReference page. It was likely altered for improvements or editors' preference. Click "Edit this page" to see all changes made to this document.
Hover to see the original license.