注意，要使用向量，則程式的標頭檔案必須指明使用 namespacestd，因為向量包含在該名稱空間中。許多較早的編譯器不允許名稱空間或不支援 STL。
在 STL 中定義的資料型別通常稱為容器。之所以稱為容器，是因為它們儲存和組織資料。STL 中有兩種型別的容器:順序容器和關聯容器：#include <vector>
建立向量物件的語法與定義一個常規變數或陣列所用的語法有所不同。以下是一個例子：vector<int> numbers;
這個語句將 numbers 定義為一個 int 的向量。請注意，資料型別包含在尖括號內，緊跟在單詞 vector 之後。由於向量的大小隨著新增值而擴大，因此不需要宣告大小。不過，如果願意的話，也可以宣告一個開始大小。範例如下：vector<int> numbers(10);
這個語句將 numbers 定義為 10 個整數的向量，但這只是一個起始大小。如果新增 10 個以上的值，它的大小將會擴大。注意，如果為向量指定開始大小，則大小宣告符將被括在圓括號中，而不是方括號。
為向量指定開始大小時，還可以指定一個初始化值。初始化值被複製到每個元素。範例如下：vector<int> numbers (10, 2);
在這個語句中，numbers 被定義為 10 個整數的向量，並且 numbers 中的每個元素都被初始化為值 2。vector<int> set2(set1);
在執行這個語句之後，向量 set2 將具有相同數量的元素，並保持與 set1 相同的一組值。如果使用的是 C++ 11 版本，則還可以使用一個值列表來初始化 vector，範例如下：vector<int> numbers { 10, 20, 30, 40 };
該語句定義了一個名為 numbers 的 int 向量。該向量有 4 個元素，其初始化值為 10, 20, 30 和 40。注意，初始化列表被括在一組大括號中，但是在它前面不使用賦值運算子(=)。表 1 總結了前面討論的向量定義過程。| 定義格式 | 描 述 |
|---|---|
| vector<string> names; | 將 names 定義為 string 物件的空向量 |
| vector<int> scores (15); | 將 scores 定義為 15 個整數的向量 |
| vector<char> letters (25, 'A'); | 將 letters 定義為 25 個字元的向量。每個元素都用 'A' 初始化 |
| vector<double> values2(values1); | 將 values2 定義為 double 向量。value1 的所有元素（也是 double 向量）將被複製到 value2 |
| vector<int> length{12, 10, 6}; | 在 C++ 11 中，該語句定義 length 為 3 個 int 值的向量，儲存值 12、10 和 6 |
//This program stores employee hours worked
// and hourly pay rates in two parallel vectors.
#include <iostream>
#include <iomanip>
#include <vector> // Needed to use vectors
using namespace std;
int main()
{
const int NUM_EMPS = 5; // Number of employees
vector <int> hours(NUM_EMPS); // Define a vector of integers
vector <double> payRate(NUM_EMPS); // Define a vector of doubles
double grossPay; // An employee's gross pay
// Get employee work data
cout << "Enter the hours worked and hourly pay rates of " << NUM_EMPS << " employees. n";
for (int index = 0; index < NUM_EMPS; index++)
{
cout <<"nHours worked by employee #" << (index + 1) << ": ";
cin >> hours[index];
cout << "Hourly pay rate for employee #" << (index +1) << ": ";
cin >> payRate[index];
}
//Display each employeeA s gross pay
cout << "nHere is the gross pay for each employee: n" ;
cout << fixed << showpoint << setprecision (2);
for (int index = 0; index < NUM_EMPS; index++)
{
grossPay = hours[index] * payRate[index];
cout << "Employee #" << (index + 1);
cout << ": $" << setw(7) << grossPay << endl;
}
return 0;
}
程式輸出結果為：
Enter the hours worked and hourly pay rates of 5 employees.
Hours worked by employee #1: 10
Hourly pay rate for employee #1: 9.75
Hours worked by employee #2: 15
Hourly pay rate for employee #2: 8.62
Hours worked by employee #3: 20
Hourly pay rate for employee #3: 10.50
Hours worked by employee #4: 40
Hourly pay rate for employee #4: 18.75
Hours worked by employee #5: 40
Hourly pay rate for employee #5: 15.65
Here is the gross pay for each employee:
Employee #1: $ 97.50
Employee #2: $ 129.30
Employee #3: $ 210.00
Employee #4: $ 750.00
Employee #5: $ 626.00
#include <vector>
在第 11 行和第 12 行中的以下語句定義了兩個向量：
vector<int> hours (NUM_EMPS) ; // 定義整數向量
vector<double> payRate (NUM_EMPS) ; // 定義雙精度型別向量
cin >> hours[index];
cin >> payRate [index];
grossPay = hours[index] * payRate[index];
只要向量已經定義並且擁有給定的起始元素，就可以像使用陣列一樣存取它們，儲存和檢索其資料。// This program uses two range-based for loops with a vector.
#include <iostream>
#include <vector>
using namespace std;
int main()
{
// Define a vector with a starting size of 5 elements
vector<int>numbers(5);
// Get values for the vector elements
// Make the range variable a reference variable so it can be
// used to change the contents of the element it references.
for (int &val : numbers)
{
cout << "Enter an integer value: ";
cin >> val;
}
// Display the vector elements
cout << "nHere are the values you entered: n";
for (int val : numbers)
cout <<val <<" ";
cout << endl;
return 0;
}
程式輸出結果：
Enter an integer value: 10
Enter an integer value: 20
Enter an integer value: 30
Enter an integer value: 40
Enter an integer value: 50
Here are the values you entered:
10 20 30 40 50
numbers.push_back(25);
該語句可以建立一個新的元素，其儲存的值為 25，該元素被放在 numbers 向量的末尾。如果 numbers 以前沒有元素，則新元素將成為其單一元素。// This program stores employee hours worked and hourly pay rates
// in two vectors. It demonstrates the use of the push_back member
// function to add new elements to the vectors.
#include <iostream>
#include <iomanip>
#include <vector>
// Needed to use vectors
using namespace std;
int main()
{
vector<int> hours; // hours is an empty integer vector
vector<double> payRate; // payRate is an empty double vector
double grossPay;
int numEmp1oyees; // Number of employees
int index; // Loop counter
// Get the number of employees
cout << "How many employees do you have?";
cin >> numEmp1oyees;
// Input the payroll data
cout << "Enter the hours worked and hourly pay rates of the "<< numEmployees << " employees. n" ;
for (index = 0; index < numEmployees; index++)
{
int tempHours; // Number of hours entered
double tempRate; 丨丨 Pay rate entered
cout << "Hours worked by employee #" << (index + 1) << ":";
cin >> tempHours;
hours.push_back(tempHours); // Add an element to hours
cout << "Hourly pay rate for employee #" << (index + 1) << ": ";
cin >> tempRate;
payRate.push_back(tempRate); // Add an element to payRate
}
//Display each employeeT s gross pay
cout << "nHere is the gross pay for each employee: n";
cout << fixed << showpoint << setprecision (2);
for (index = 0; index < numEmployees; index++)
{
grossPay = hours[index] * payRate[index];
cout << "Employee #" << (index + 1);
cout << " $" << setw (7) << grossPay << endl;
}
return 0;
}
程式輸出結果：
How many employees do you have?3
Enter the hours worked and hourly pay rates of the 3 employees.
Hours worked by employee #1:40
Hourly pay rate for employee #1: 12.63
Hours worked by employee #2:25
Hourly pay rate for employee #2: 10.35
Hours worked by employee #3:45
Hourly pay rate for employee #3: 22.65
Here is the gross pay for each employee:
Employee #1 $ 505.20
Employee #2 $ 258.75
Employee #3 $1019.25
numValues = set.size();
在該語句中，假定 numValues 是一個 int，set 是一個向量。執行語句後，numValues 將包含 set 中的元素數量。void showValues(vector<int> vect)
{
for (int count = 0; count < vect.size(); count++)
cout << vect[count] << endl;
}
因為向量可以報告其大小，所以該函數不需要第二個引數來表示向量中元素的個數。下面的程式演示了該函數的應用：
//This program demonstrates the vector size member function.
#include <iostream>
#include <vector>
using namespace std;
// Function prototype
void showValues(vector<int>);
int main()
{
vector<int> values;
// Store a series of numbers in the vector
for (int count = 0; count < 7; count++)
values.push_back(count * 2);
// Display the numbers
showValues(values);
return 0;
}
void showValues(vector<int> vect)
{
for (int count = 0; count < vect.size(); count++)
cout << vect[count] << " ";
cout << endl;
}
程式輸出結果：
0 2 4 6 8 10 12
程式中在定義向量時，並未給定元素，所以在將值儲存到向量中時，使用了 push_back 函數。每次被呼叫時，push_back 函數都將建立一個新的向量元素來儲存值。collection.pop_back();
下面的程式演示了 pop_back 函數：//This program demonstrates the vector size,
//push_back, and pop_back member functions.
#include <iostream>
#include <vector>
using namespace std;
int main()
{
vector<int> values;
// Store values in the vector
values.push_back(1);
values.push_back(2);
values.push_back(3);
cout << "The size of values is " << values.size () << endl;
// Remove a value from the vector
cout << "Popping a value from the vector...n";
values.pop_back();
cout << "The size of values is now " << values.size () << endl;
// Now remove another value from the vector
cout << "Popping a value from the vector...n";
values.pop_back();
cout << "The size of values is now " << values.size() << endl;
// Remove the last value from the vector
cout << "Popping a value from the vector...n"; values.pop_back();
cout << "The size of values is now " << values.size () << endl;
return 0;
}
程式輸出結果：
The size of values is 3
Popping a value from the vector...
The size of values is now 2
Popping a value from the vector...
The size of values is now 1
Popping a value from the vector...
The size of values is now 0
cout << "The value being removed from the vector is "<<values.pop_back() << endl; // Error!
numbers.clear();
在執行該語句之後，numbers 的所有元素都將被清除。下面的程式演示了該函數的用法：//This program demonstrates the vector clear member function.
#include <iostream>
#include <vector>
using namespace std;
int main()
{
vector<int> values(100);
cout << "The values vector has " << values.size() << " elements.n";
cout << "will call the clear member function. . . n";
values.clear();
cout << "Now the values vector has "<< values.size() << " elements . n";
return 0;
}
程式輸出結果：
The values vector has 100 elements.
will call the clear member function. . .
Now the values vector has 0 elements .
if (numberVector.empty())
cout << "No values in numberVector. n";
下面的程式顯示了如何傳遞一個向量給函數。該函數名為 avgVector，演示了 empty 成員函數的用法。
//This program demonstrates the vector empty member function.
#include <iostream>
#include <vector>
using namespace std;
// Function prototype
double avgVector(vector<int>);
int main()
{
vector<int> values; // Define a vector to hold int values
int numValues; // Number of values to be averaged
double average; // Average of the stored values
//Get the number of values to average
cout << "How many values do you wish to average?";
cin >> numValues;
// Get the values and store them in a vector
for (int count = 0; count < numValues; count++)
{
int tempValue;
cout << "Enter an integer value:";
cin >> tempValue;
values.push_back(tempValue);
}
// Get the average of the values and display it
average = avgVector(values);
cout << "Average: " << average << endl;
return 0;
}
double avgVector(vector<int> vect)
{
int total = 0; // Accumulator
double avg = 0.0;
if (vect.empty()) // Determine if the vector is empty
cout << "No values to average. n";
else
{
for (int count = 0; count < vect.size(); count++)
total += vect[count];
avg = static_cast<double>(total)/vect.size();
}
return avg;
}
程式輸出結果：
How many values do you wish to average?4
Enter an integer value:12
Enter an integer value:3
Enter an integer value:7
Enter an integer value:9
Average: 7.75
| 成員函數 | 描 述 |
|---|---|
| at(position) |
返回 vector 中位於 position 位置的兀素的值。範例： x = vect. at (5) ; //將 vect [5] 的值賦給 x |
| capacity() |
返回在不重新分配額外記憶體的情況下，可能儲存在向量中的最大元素數量(它和由 size 成員函數返回的值並不是一回事)。範例： x = vect. capacity () ; //將 vect 的容量賦值給 x |
| clear() |
清除向量的所有元素。範例： vect .clear () ; //從 vect 中移除所有兀素 |
| empty() |
如果 vector 是空的，則返回 true。否則，它返回 false。範例： if (vect. empty () ; //如果該向量是空的 cout << "The vector is empty."; |
| pop_back() |
從向量中刪除最後一個元素。範例： vect.pop_back () ; //移除 vect 的最後一個元素，大小減去1 |
| push_back(value) |
在向量的最後一個元素中儲存一個值。如果向量已滿或為空，則會建立一個 新元素。範例： vect.push_back (7) ; //在 vect 的最後一個元素中儲存 7 |
| reverse() |
反轉向量中元素的順序（最後一個元素變成第一個元素，第一個元素成為最後一個元素)。範例： vect. reverse () ; //反轉 vect 中元素的順序 |
|
resize(n) resize(n, value) |
調整向量的大小以使其具有 n 個元素，其中 n 大於向量的當前大小。如果包含可選的引數 value，則每個新元素都將使用該 value 值進行初始化。 vect 當前已有 4 個元素情況下的範例： vect. resize (6, 99) ; //將兩個元素新增到向量的末尾，每個元素初始化為 99 |
| size() |
返回向量中元素的數量。範例： numElements = vect.size(); |
| swap(vector2) |
將向量的內容與 vector2 的內容交換。範例： vect1.swap (vect2) ; //交換 vect1 和 vect2 的內容 |