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法律研究C++中的vector::resize()与vector::reserve()
当插入或删除元素时，vector能够自动调整自身大小，如同动态数组一样，容器会自动处理它们的存储。
vector resize()和vector reserve()的主要区别在于，resize()用于改变vector的大小，而reserve()不。reserve()仅用于储存至少指定数量的元素，而无需重新分配内存。但是在resize()中，如果指定数量小于当前数量，它会重新调整内存大小，并删除多余的空间。
vector::resize()
Vector resize()用于改变其大小。
示例
源代码中的步骤
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;
}输出
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()表示创建的vector至少可以储存指定数量的元素，而无需重新分配内存。
源代码中的步骤
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;
}输出
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
更新时间： 30-Jul-2019
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