Difference between revisions of "cpp/string/basic string/substr"
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< cpp | string | basic string
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| − | {{ | + | {{dcl begin}} |
| − | basic_string substr( size_type pos = 0, | + | {{dcl rev multi | until1=c++20 | dcl1= |
| − | + | basic_string substr( size_type pos = 0, size_type count = npos ) const; | |
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| + | constexpr basic_string substr( size_type pos = 0, size_type count = npos ) const; | ||
}} | }} | ||
| + | {{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()}}]]{{tt|)}}. | ||
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Revision as of 22:26, 19 February 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()).
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()) 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); 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 |
