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時裝研究
法律研究C++中的vector::resize()與vector::reserve()
當插入或刪除元素時，vector能夠自動調整自身大小，如同動態陣列一樣，容器會自動處理它們的儲存。
vector resize()和vector reserve()的主要區別在於，resize()用於改變vector的大小，而reserve()不。reserve()僅用於儲存至少指定數量的元素，而無需重新分配記憶體。但是在resize()中，如果指定數量小於當前數量，它會重新調整記憶體大小，並刪除多餘的空間。
vector::resize()
Vector resize()用於改變其大小。
示例
原始碼中的步驟
Begin Declare a variable v of vector type. Declare another variable it as iterator of vector type. Declare another two variable c and i of the integer datatype. while (1) do print “1.Size of the Vector”. print “2.Insert Element into the Vector”. print “3.Resize the vector”. print “4.Display by Iterator”. print “5.Exit”. print “Enter your Choice:”. Enter the value of variable c. Switch(c) Case 1. Print “Size of Vector:”. Call size() function to print the size of the vector. Break. Case 2. Print “Enter value to be inserted:”. Enter the value of variable i. Call push_back() function to input the values in the vector. Break. Case 3. Print “Resize the vector elements:”. Call resize() function to resize the vector. Break. Case 4. Print “Displaying Vector by Iterator:”. for (it = v.begin(); it != v.end(); it++) print the value of iterator it. Break. case 5. call exit() function to take exit. break. Default. Print “Wrong choice”. End.
示例
#include <iostream>
#include <vector>
using namespace std;
int main() {
vector<int> v;
vector<int>::iterator it;
int c, i;
while (1) {
cout<<"1.Size of the Vector"<<endl;
cout<<"2.Insert Element into the Vector"<<endl;
cout<<"3.Resize the vector"<<endl;
cout<<"4.Display by Iterator"<<endl;
cout<<"5.Exit"<<endl;
cout<<"Enter your Choice: ";
cin>>c;
switch(c) {
case 1:
cout<<"Size of Vector: ";
cout<<v.size()<<endl; //printing the size of vector
break;
case 2:
cout<<"Enter value to be inserted: ";
cin>>i;
v.push_back(i); //inserting values
break;
case 3:
cout<<"Resize the vector elements:"<<endl;
v.resize(4); / /resize the vector
break;
case 4:
cout<<"Displaying Vector by Iterator: ";
for (it = v.begin(); it != v.end(); it++) //printing all values of the vector {
cout<<*it<<" ";
}
cout<<endl;
break;
case 5:
exit(1);
break;
default:
cout<<"Wrong Choice"<<endl;
}
}
return 0;
}輸出
1.Size of the Vector 2.Insert Element into the Vector 3.Resize the vector 4.Display by Iterator 5.Exit Enter your Choice: 1 Size of Vector: 0 1.Size of the Vector 2.Insert Element into the Vector 3.Resize the vector 4.Display by Iterator 5.Exit Enter your Choice: 2 Enter value to be inserted: 1 1.Size of the Vector 2.Insert Element into the Vector 3.Resize the vector 4.Display by Iterator 5.Exit Enter your Choice: 2 Enter value to be inserted: 2 1.Size of the Vector 2.Insert Element into the Vector 3.Resize the vector 4.Display by Iterator 5.Exit Enter your Choice: 2 Enter value to be inserted: 4 1.Size of the Vector 2.Insert Element into the Vector 3.Resize the vector 4.Display by Iterator 5.Exit Enter your Choice: 2 Enter value to be inserted: 5 1.Size of the Vector 2.Insert Element into the Vector 3.Resize the vector 4.Display by Iterator 5.Exit Enter your Choice: 2 Enter value to be inserted: 5 1.Size of the Vector 2.Insert Element into the Vector 3.Resize the vector 4.Display by Iterator 5.Exit Enter your Choice: 4 Displaying Vector by Iterator: 1 2 4 5 5 1.Size of the Vector 2.Insert Element into the Vector 3.Resize the vector 4.Display by Iterator 5.Exit Enter your Choice: 3 Resize the vector elements: 1.Size of the Vector 2.Insert Element into the Vector 3.Resize the vector 4.Display by Iterator 5.Exit Enter your Choice: 4 Displaying Vector by Iterator: 1 2 4 5 1.Size of the Vector 2.Insert Element into the Vector 3.Resize the vector 4.Display by Iterator 5.Exit Enter your Choice: 5
vector::reserve()
vector reserve()表示建立的vector至少可以儲存指定數量的元素，而無需重新分配記憶體。
原始碼中的步驟
Begin Declare a variable v of vector type. Declare another variable it as iterator of vector type. Declare another two variable c and i to the ineger datatype. while (TRUE) do print “1.Size of the Vector”. print “2.Insert Element into the Vector”. print “3.Reserve the vector”. print “4.Display by Iterator”. print “5.Exit”. print “Enter your Choice:”. Enter the value of variable c. Switch(c) Case 1. Print “Size of Vector:”. Call size() function to print the size of the vector. Break. Case 2. Print “Enter value to be inserted:”. Enter the value of variable i. Call push_back() function to input the values in the vector. Break. Case 3. Print “Reserve the vector elements:”. Call reserve() function to reserve the size of the vector. Break. Case 4. Print “Displaying Vector by Iterator:”. for (it = v.begin(); it != v.end(); it++) print the value of iterator it. Break. case 5. call exit() function to take exit. break. Default. Print “Wrong choice”. End.
示例
#include <iostream>
#include <vector>
using namespace std;
int main() {
vector<int> v;
vector<int>::iterator it;
int c, i;
while (1) {
cout<<"1.Size of the Vector"<<endl;
cout<<"2.Insert Element into the Vector"<<endl;
cout<<"3.Reserve the vector"<<endl;
cout<<"4.Display by Iterator"<<endl;
cout<<"5.Exit"<<endl;
cout<<"Enter your Choice: ";
cin>>c;
switch(c) {
case 1:
cout<<"Size of Vector: ";
cout<<v.size()<<endl;
break;
case 2:
cout<<"Enter value to be inserted: ";
cin>>i;
v.push_back(i);
break;
case 3:
cout<<"Reserve the vector elements:"<<endl;
v.reserve(100); //reserve the vector elements
break;
case 4:
cout<<"Displaying Vector by Iterator: ";
for (it = v.begin(); it != v.end(); it++) {
cout<<*it<<" ";
}
cout<<endl;
break;
case 5:
exit(1);
break;
default:
cout<<"Wrong Choice"<<endl;
}
}
return 0;
}輸出
1.Size of the Vector 2.Insert Element into the Vector 3.Reserve the vector 4.Display by Iterator 5.Exit Enter your Choice: 1 Size of Vector: 0 1.Size of the Vector 2.Insert Element into the Vector 3.Reserve the vector 4.Display by Iterator 5.Exit Enter your Choice: 2 Enter value to be inserted: 1 1.Size of the Vector 2.Insert Element into the Vector 3.Reserve the vector 4.Display by Iterator 5.Exit Enter your Choice: 2 Enter value to be inserted: 2 1.Size of the Vector 2.Insert Element into the Vector 3.Reserve the vector 4.Display by Iterator 5.Exit Enter your Choice: 2 Enter value to be inserted: 3 1.Size of the Vector 2.Insert Element into the Vector 3.Reserve the vector 4.Display by Iterator 5.Exit Enter your Choice: 2 Enter value to be inserted: 4 1.Size of the Vector 2.Insert Element into the Vector 3.Reserve the vector 4.Display by Iterator 5.Exit Enter your Choice: 2 Enter value to be inserted: 5 1.Size of the Vector 2.Insert Element into the Vector 3.Reserve the vector 4.Display by Iterator 5.Exit Enter your Choice: 3 Reserve the vector elements: 1.Size of the Vector 2.Insert Element into the Vector 3.Reserve the vector 4.Display by Iterator 5.Exit Enter your Choice: 4 Displaying Vector by Iterator: 1 2 3 4 5 1.Size of the Vector 2.Insert Element into the Vector 3.Reserve the vector 4.Display by Iterator 5.Exit Enter your Choice: 4 Displaying Vector by Iterator: 1 2 3 4 5 1.Size of the Vector 2.Insert Element into the Vector 3.Reserve the vector 4.Display by Iterator 5.Exit
更新時間： 30-Jul-2019
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