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Add C++20 "starts_with" overloads

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Ion Gaztañaga
2026-01-21 23:40:18 +01:00
parent a02aae0b9f
commit dc3a96a29b
3 changed files with 41 additions and 22 deletions
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2
doc/container.qbk
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@@ -1461,7 +1461,7 @@ use [*Boost.Container]? There are several reasons for that:
* Implemented overaligned allocation support for `adaptive_pool`and `node_allocator`
* Updated `basic_string` to the latest standard API:
* Added missing `string_view` members and updated `operator[]` to be able to return the terminating null.
* Added C++23 `contains` overloads
* Added C++20 `starts_with` and C++23 `contains` overloads.
* Fixed bugs/issues:
* [@https://github.com/boostorg/container/issues/323 GitHub #323: ['"flat_tree::try_emplace UB"]].
* [@https://github.com/boostorg/container/issues/328 GitHub #328: ['"boost::container::deque stores a redundant copy of the allocator, increasing size"]].

32
include/boost/container/string.hpp
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@@ -2981,6 +2981,38 @@ class basic_string
bool contains(const CharT* s) const BOOST_NOEXCEPT
{ return this->find(s) != npos; }
//! <b>Effects</b>: Checks if the string begins with the given prefix
//!
//! <b>Throws</b>: Nothing
//!
//! <b>Returns</b>: true if the string begins with the provided prefix, false otherwise.
template<template <class, class> class BasicStringView>
BOOST_CONTAINER_NODISCARD inline
bool starts_with(BasicStringView<CharT, Traits> sv) const BOOST_NOEXCEPT
{ return this->size() >= sv.size() && Traits::compare(this->data(), sv.data(), sv.size()) == 0; }
//! <b>Effects</b>: Checks if the string begins with the given prefix
//!
//! <b>Throws</b>: Nothing
//!
//! <b>Returns</b>: true if the string begins with the provided prefix, false otherwise.
BOOST_CONTAINER_NODISCARD inline
bool starts_with(CharT c) const BOOST_NOEXCEPT
{ return !empty() && Traits::eq(front(), c); }
//! <b>Effects</b>: Checks if the string begins with the given prefix
//!
//! <b>Throws</b>: Nothing
//!
//! <b>Returns</b>: true if the string begins with the provided prefix, false otherwise.
BOOST_CONTAINER_NODISCARD inline
bool starts_with(const CharT* s) const BOOST_NOEXCEPT
{
const size_type s_sz = Traits::length(s);
const size_type t_sz = this->size();
return t_sz >= s_sz && Traits::compare(this->data(), s, s_sz) == 0;
}
#ifndef BOOST_CONTAINER_DOXYGEN_INVOKED
private:
void priv_move_assign(BOOST_RV_REF(basic_string) x, dtl::bool_<true> /*steal_resources*/)

29
test/string_test.cpp
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@@ -1481,13 +1481,7 @@ void test_compare()
// Helper functions for starts_with/ends_with/contains since boost::container::string
// might not have these methods in older versions
namespace test_helpers {
bool starts_with(const string& s, const char* prefix) {
string::size_type len = std::strlen(prefix);
return s.size() >= len && s.compare(0, len, prefix) == 0;
}
bool starts_with(const string& s, char c) {
return !s.empty() && s[0] == c;
}
bool ends_with(const string& s, const char* suffix) {
string::size_type len = std::strlen(suffix);
return s.size() >= len && s.compare(s.size() - len, len, suffix) == 0;
@@ -1495,27 +1489,20 @@ namespace test_helpers {
bool ends_with(const string& s, char c) {
return !s.empty() && s[s.size() - 1] == c;
}
bool contains(const string& s, const char* substr) {
return s.find(substr) != string::npos;
}
bool contains(const string& s, char c) {
return s.find(c) != string::npos;
}
}
void test_starts_with()
{
string s("Hello, World!");
using test_helpers::starts_with;
BOOST_TEST(starts_with(s, "Hello"));
BOOST_TEST(starts_with(s, "H"));
BOOST_TEST(starts_with(s, ""));
BOOST_TEST(starts_with(s, 'H'));
BOOST_TEST(s.starts_with("Hello"));
BOOST_TEST(s.starts_with("H"));
BOOST_TEST(s.starts_with(""));
BOOST_TEST(s.starts_with('H'));
BOOST_TEST(!starts_with(s, "World"));
BOOST_TEST(!starts_with(s, "hello")); // case-sensitive
BOOST_TEST(!starts_with(s, 'W'));
BOOST_TEST(!s.starts_with("World"));
BOOST_TEST(!s.starts_with("hello")); // case-sensitive
BOOST_TEST(!s.starts_with('W'));
}
void test_ends_with()