Difference between revisions of "cpp/string/basic string/substr"
From cppreference.com
< cpp | string | basic string
(P0980R1, remove std::string:: since it requires a specified specialization (std::basic_string::npos might be better but it's invalid)) |
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{{dcl end}} | {{dcl end}} | ||
| − | Returns a substring {{tt|[pos, pos+count)}}. If the requested substring extends past the end of the string, or if {{c|1=count == npos}}, the returned substring is {{tt|[pos, }}[[cpp/string/basic_string/size|{{tt|size()}}]]{{tt|)}}. | + | Returns a substring {{tt|[pos, pos+count)}}. If the requested substring extends past the end of the string, or if {{c|1=count == npos}}, the returned substring is {{tt|[pos, }}[[cpp/string/basic_string/size|{{tt|size()}}]]-pos{{tt|)}}. |
===Parameters=== | ===Parameters=== | ||
| Line 40: | Line 40: | ||
std::string a = "0123456789abcdefghij"; | std::string a = "0123456789abcdefghij"; | ||
| − | // count is npos, returns [pos, size()) | + | // count is npos, returns [pos, size()-pos) |
std::string sub1 = a.substr(10); | std::string sub1 = a.substr(10); | ||
std::cout << sub1 << '\n'; | std::cout << sub1 << '\n'; | ||
| Line 48: | Line 48: | ||
std::cout << sub2 << '\n'; | std::cout << sub2 << '\n'; | ||
| − | // pos is within bounds, pos+count is not, returns [pos, size()) | + | // pos is within bounds, pos+count is not, returns [pos, size()-pos) |
std::string sub4 = a.substr(a.size()-3, 50); | std::string sub4 = a.substr(a.size()-3, 50); | ||
std::cout << sub4 << '\n'; | std::cout << sub4 << '\n'; | ||
Revision as of 06:11, 18 September 2020
basic_string substr( size_type pos = 0, size_type count = npos ) const; |
(until C++20) | |
| constexpr basic_string substr( size_type pos = 0, size_type count = npos ) const; |
(since C++20) | |
Returns a substring [pos, pos+count). If the requested substring extends past the end of the string, or if count == npos, the returned substring is [pos, size()-pos).
Contents |
Parameters
| pos | - | position of the first character to include |
| count | - | length of the substring |
Return value
String containing the substring [pos, pos+count).
Exceptions
std::out_of_range if pos > size()
Complexity
Linear in count
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 will not be a copy of this->get_allocator().
Example
Run this code
#include <string> #include <iostream> int main() { std::string a = "0123456789abcdefghij"; // count is npos, returns [pos, size()-pos) 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()-pos) std::string sub4 = a.substr(a.size()-3, 50); 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
See also
| copies characters (public member function) | |
| returns the number of characters (public member function) | |
| finds the first occurrence of the given substring (public member function) | |
constexpr size_type npos [static]
|
the special value size_type(-1), its exact meaning depends on the context |
