C++中常用库函数
C++中常用库函数
1 字符串处理
1.1 字符串查找: strstr
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#include <string.h>
#include <stdio.h>
void find_str(char const* str, char const* substr)
{
char* pos = strstr(str, substr);
if(pos) {
printf("found the string '%s' in '%s' at position: %ld\n", substr, str, pos - str);
} else {
printf("the string '%s' was not found in '%s'\n", substr, str);
}
}
int main(void)
{
char* str = "one two three";
find_str(str, "two");
find_str(str, "");
find_str(str, "nine");
find_str(str, "n");
return 0;
}
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2 algorithm库
2.1 排序
2.1.1 sort
Sorts the elements in the range [first, last) in ascending order. The order of equal elements is not guaranteed to be preserved.
说明：sort函数默认将数据按照升序排列。
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// template< class RandomIt >
// void sort( RandomIt first, RandomIt last );
std::array<int, 10> s = {5, 7, 4, 2, 8, 6, 1, 9, 0, 3};
// sort using the default operator<
std::sort(s.begin(), s.end());
// 自定义比较函数，实现降序排序
// sort using a custom function object
struct {
bool operator()(int a, int b)
{
return a < b;
}
} customLess;
std::sort(s.begin(), s.end(), customLess);
for (auto a : s) {
std::cout << a << " ";
}
std::cout << '\n';
// sort using a lambda expression
std::sort(s.begin(), s.end(), [](int a, int b) {
return b < a;
});
for (auto a : s) {
std::cout << a << " ";
}
std::cout << '\n';
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2.1.2 stable_sort()
说明：Sorts the elements in the range [first, last) in ascending order. The order of equal elements is guaranteed to be preserved.
2.1.3 partial_sort()
Rearranges elements such that the range [first, middle) contains the sorted middle - first smallest elements in the range [first, last).
The order of equal elements is not guaranteed to be preserved. The order of the remaining elements in the range [middle, last) is unspecified.
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std::array<int, 10> s{5, 7, 4, 2, 8, 6, 1, 9, 0, 3};
std::partial_sort(s.begin(), s.begin() + 3, s.end());
for (int a : s) {
std::cout << a << " ";
}
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2.2 二分查找
2.2.1 binary_search()
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// template< class ForwardIt, class T>
// bool binary_search( ForwardIt first, ForwardIt last, const T& value ); (1)
// template< class ForwardIt, class T, class Compare >
// bool binary_search( ForwardIt first, ForwardIt last, const T& value, Compare comp ); (2)
// 示例
std::vector<int> haystack {1, 3, 4, 5, 9};
std::vector<int> needles {1, 2, 3};
for (auto needle : needles) {
std::cout << "Searching for " << needle << '\n';
if (std::binary_search(haystack.begin(), haystack.end(), needle)) {
std::cout << "Found " << needle << '\n';
} else {
std::cout << "no dice!\n";
}
}
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2.2.2 lower_bound()
功能说明：Returns an iterator pointing to the first element in the range [first, last) that is not less than (i.e. greater or equal to) value.
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// template< class ForwardIt, class T >
// ForwardIt lower_bound( ForwardIt first, ForwardIt last, const T& value );
// template< class ForwardIt, class T, class Compare >
// ForwardIt lower_bound( ForwardIt first, ForwardIt last, const T& value, Compare comp );
std::vector<int> data = { 1, 1, 2, 3, 3, 3, 3, 4, 4, 4, 5, 5, 6 };
auto lower = std::lower_bound(data.begin(), data.end(), 4);
auto upper = std::upper_bound(data.begin(), data.end(), 4);
std::copy(lower, upper, std::ostream_iterator<int>(std::cout, " ")); // 4 4 4
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2.2.3 upper_bound()
Returns an iterator pointing to the first element in the range [first, last) that is greater than value.
2.3 revert()
接口定义：
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template< class BidirIt > void reverse( BidirIt first, BidirIt last );
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示例：
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std::vector<int> v({1,2,3});
std::reverse(std::begin(v), std::end(v));
std::cout << v[0] << v[1] << v[2] << '\n';
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2.4 heap
2.4.1 make_heap()
接口定义：
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template< class RandomIt> void make_heap(RandomIt first, RandomIt last);
template< class RandomIt, class Compare> void make_heap(RandomIt first, RandomIt last, Compare comp);
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示例：
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std::vector<int> v = {3, 1, 4, 1, 5, 9};
std::make_heap(v.begin(), v.end());
// heap: 9 4 5 1 1 3
std::cout << "heap:\t";
for (const auto &i : v) {
std::cout << i << ' ';
}
std::sort_heap(v.begin(), v.end());
// sorted: 1 1 3 4 5 9
std::cout << "\nsorted:\t";
for (const auto &i : v) {
std::cout << i << ' ';
}
std::cout << '\n';
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2.4.2 sort_heap()
接口定义：
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template< class RandomIt > void sort_heap( RandomIt first, RandomIt last);
template< class RandomIt, class Compare > void sort_heap( RandomIt first, RandomIt last, Compare comp);
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2.4.3 push_heap()
接口定义：
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template< class RandomIt >
void push_heap( RandomIt first, RandomIt last );
template< class RandomIt, class Compare>
void push_heap(RandomIt first, RandomIt last, Compare comp );
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示例：
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std::vector<int> v { 3, 1, 4, 1, 5, 9 };
std::make_heap(v.begin(), v.end());
std::cout << "v: "; // v: 9 5 4 1 1 3
for (auto i : v) std::cout << i << ' ';
std::cout << '\n';
v.push_back(6);
std::cout << "before push_heap: "; // before push_heap: 9 5 4 1 1 3 6
for (auto i : v) std::cout << i << ' ';
std::cout << '\n';
std::push_heap(v.begin(), v.end());
std::cout << "after push_heap: "; // after push_heap: 9 5 6 1 1 3 4
for (auto i : v) std::cout << i << ' ';
std::cout << '\n';
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2.4.4 pop_heap()
示例：
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std::vector<int> v { 3, 1, 4, 1, 5, 9 };
std::make_heap(v.begin(), v.end());
std::cout << "v: "; // v: 9 5 4 1 1 3
for (auto i : v) std::cout << i << ' ';
std::cout << '\n';
std::pop_heap(v.begin(), v.end()); // moves the largest to the end
std::cout << "after pop_heap: "; // after pop_heap: 5 3 4 1 1 9
for (auto i : v) std::cout << i << ' ';
std::cout << '\n';
int largest = v.back();
v.pop_back(); // actually removes the largest element
std::cout << "largest element: " << largest << '\n'; // largest element: 9
std::cout << "heap without largest: "; // heap without largest: 5 3 4 1 1
for (auto i : v) std::cout << i << ' ';
std::cout << '\n';
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