stl reserve

C ++ vector :: reserve()函數(shù) (C++ vector::reserve() function)

vector::reserve() is a library function of "vector" header, which is used to request change in vector allocation. Refer to example to understand in details.

vector :: reserve()是“ vector”頭的庫函數(shù)，用于請(qǐng)求矢量分配的更改。 請(qǐng)參閱示例以詳細(xì)了解。

Note: To use vector, include <vector> header.

注意：要使用向量，請(qǐng)包含<vector>標(biāo)頭。

Syntax of vector::reserve() function

vector :: reserve()函數(shù)的語法

vector::reserve(n);

Parameter(s): int n – It accepts n as a parameter where n be the input capacity.

參數(shù)： int n –接受n作為參數(shù)，其中n是輸入容量。

Return value: void – It returns nothing in case of valid request. But if the capacity requested is greater than the maximum size of the vector (vector::max_size), a length_error exception is thrown.

返回值： void –在有效請(qǐng)求的情況下不返回任何內(nèi)容。 但是，如果請(qǐng)求的容量大于向量的最大大小( vector :: max_size )，則會(huì)引發(fā)length_error異常。

Example: Case 1: (without reserve())

示例：情況1 ：(沒有reserve())

vector<int> arr1; //usual dynamic allocation size = arr1.capacity(); cout << "arr1 growing with usual dynamic allocation:\n"; for (int i = 0; i < 50; ++i) {arr1.push_back(i);if (size != arr1.capacity()) {size = arr1.capacity();cout << "capacity changed to : " << size << '\n';} }

In this case, we have not used reserve thus the growth is as per dynamic allocation, which increases in a factor of two. Like, 1, 2, 4, 8, 16, 32, 64, 128…..so on till max_size.

在這種情況下，我們沒有使用儲(chǔ)備金，因此增長是按動(dòng)態(tài)分配進(jìn)行的，增長了兩倍。 像1，2，4，8，16，16，32，64，128…..so直到max_size 。

Example: Case 2: (with reserve())

示例：情況2 ：(帶有reserve())

vector<int> arr2; //using reserve size = arr2.capacity(); arr2.reserve(50); // use of reserve function cout << "arr2 growing with using reverse:\n"; for (int i = 0; i < 50; ++i) {arr2.push_back(i);if (size != arr2.capacity()) {size = arr2.capacity();cout << "capacity changed to: " << size << '\n';} }

In this case, we have not used reserve thus the growth is as per dynamic allocation, which increases in a factor of two. Like, 1, 2, 4, 8, 16, 32, 64, 128…..so on till max_size.

在這種情況下，我們沒有使用儲(chǔ)備金，因此增長是按動(dòng)態(tài)分配進(jìn)行的，增長了兩倍。 像1，2，4，8，16，16，32，64，128…..so直到max_size 。

C ++程序演示vector :: reserve()函數(shù)的示例 (C++ program to demonstrate example of vector::reserve() function)

#include <iostream> #include <vector>using namespace std;int main() {vector<int>::size_type size;vector<int> arr1; //usual dynamic allocationsize = arr1.capacity();cout << "arr1 growing with usual dynamic allocation:\n";for (int i = 0; i < 50; ++i) {arr1.push_back(i);if (size != arr1.capacity()) {size = arr1.capacity();cout << "capacity changed to : " << size << '\n';}}vector<int> arr2; //using reservesize = arr2.capacity();arr2.reserve(50); // use of reserve functioncout << "arr2 growing with using reverse:\n";for (int i = 0; i < 50; ++i) {arr2.push_back(i);if (size != arr2.capacity()) {size = arr2.capacity();cout << "capacity changed to: " << size << '\n';}}return 0; }

Output

輸出量

arr1 growing with usual dynamic allocation: capacity changed to : 1 capacity changed to : 2 capacity changed to : 4 capacity changed to : 8 capacity changed to : 16 capacity changed to : 32 capacity changed to : 64 arr2 growing with using reverse: capacity changed to: 50

Reference: C++ vector::reserve()

參考： C ++ vector :: reserve()

翻譯自: https://www.includehelp.com/stl/vector-reserve-function-with-example.aspx

stl reserve

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