C++ collection容器基础知识

最常见的类为vector，基本上可以取代C的array，而且比array好用很多。

下面这个例子，是从文件中读取所有的行存入到lines中，然后输出。

vector类

不用去管promptUserForFile以及readEntireFile怎么实现的，包含那个库很重要。

#include <iostream>#include <fstream>#include <string>#include "filelib.h"#include "vector.h"#include "console.h"using namespace std;void readEntireFile(istream &is, Vector<string> &lines);int main() {    ifstream infile;    Vector<string> lines;    promptUserForFile(infile, "Input file: ");    readEntireFile(infile, lines);    infile.close();    for (int i = lines.size() - 1; i >= 0; i--) {        cout << lines[i] << endl;    }    return 0;}

下面这个例子，统计字符

#include <iostream>#include <iomanip>#include <fstream>#include <cctype>#include "filelib.h"#include "vector.h"#include "console.h"using namespace std;static const int COLUMNS = 7;int main() {    Vector<int> letterCounts(26);    ifstream infile;    promptUserForFile(infile, "Input file: ");    char ch;    while (infile.get(ch)) {        if (isalpha(ch)) {            letterCounts[toupper(ch) - 'A']++;        }    }    infile.close();    for (char ch = 'A'; ch <= 'Z'; ch++) {        cout << setw(COLUMNS) << letterCounts[ch - 'A'] << " " << ch << endl;    }    return 0;}

Input file: /home/wang/3english

377 A

55 B

190 C

247 D

575 E

119 F

62 G

203 H

344 I

2 J

14 K

205 L

105 M

318 N

288 O

92 P

2 Q

253 R

364 S

389 T

108 U

34 V

53 W

32 X

60 Y

4 Z

定义两层容器，最容易想到的就是棋盘

Vector<Vector<int>> sudoku(9, Vector<int>(9));

注意>> 和> >的区别。

stack类

stack是写一个rpn计算机，这是个toy表达式，真正的计算器并不是这样实现的。

/* * This porgram simulates an electronic calculator that uses * reverse Polish notation, in which the operators come after * the operands to which they apply. Information for users * of this application appears in the helpCommand function. */#include <iostream>#include <cctype>#include <string>#include "error.h"#include "simpio.h"#include "stack.h"#include "strlib.h"#include "console.h"using namespace std;void applyOperator(char op, Stack<double> &operandStack) {    double result;    double rhs = operandStack.pop();    double lhs = operandStack.pop();    switch (op) {    case '+': result = lhs + rhs; break;    case '-': result = lhs - rhs; break;    case '*': result = lhs * rhs; break;    case '/': result = lhs / rhs; break;    default:        error("Illegal operator");    }    cout << result << endl;    operandStack.push(result);}void helpCommand() {    cout << "Enter expressions in Reverse Polish Notation." << endl;}int main() {    cout << "RPN Calculator Simulation (type H for help)" << endl;    Stack<double> operandStack;    while (true) {        string line = getLine("> ");        if (line.length() == 0) line = "Q";        char ch = toupper(line[0]);        if (ch == 'Q') {            break;        } else if (ch == 'C') {            operandStack.clear();        } else if (ch == 'H') {            helpCommand();        } else if (isdigit(ch)) {            operandStack.push(stringToReal(line));        } else {            applyOperator(ch, operandStack);        }    }    return 0;}

RPN Calculator Simulation (type H for help)

> 12

> 12

> +

24

> 12

> 12

> /

1

> +

25

>

Queue类

这个例子是排队付钱的例子，比较常见，有英文注释，可以理解这个queue

/* * This program simulate a checkout line, such as one you * might encounter in a grocery store. Customers arrive at * the checkout stand and get in line. Those customers wait * in the lines until the cashier is free, at which point * they are served and occupy the cashier for some period * of time. After the service time is complete, the cashier * is free to serve the next customer in the line. * * In each unit of time, up to the constant SIMULATION_TIME, * the following operations are performed: * 1. Detemine whether a new customer has arrived. *    New customers arrives randomly, with a probability *    determined by the constant ARRIVAL_PROBABILITY. * 2. If the cashier is busy, note that the crashier has spent *    another minute with that customer. Eventually, *    the customer's time request is satisfied, which frees the cashier. * 3. If the cashier is free, serve the next customer in line. *    The service time is taken to be a random period betweens *    MIN_SERVICE_TIME and MAX_SERVICE_TIME. * * At the end of the simulations, the program displays the simulation * constants and the following computed results: *  The number of customers served *  The average time spent in line *  The average number of people in line. */#include <iostream>#include <iomanip>#include "queue.h"#include "random.h"using namespace std;const double ARRIVAL_PROBABILITY = 0.05;const int MIN_SERVICE_TIME = 5;const int MAX_SERVICE_TIME = 15;const int SIMULATION_TIME = 2000;void runSimulation(int &nServed, int &totalWait, int &totalLength);void printReport(int nServed, int totalWait, int totalLength);int main() {    int nServed;    int totalWait;    int totalLength;    runSimulation(nServed, totalWait, totalLength);    printReport(nServed, totalWait, totalLength);}void runSimulation(int &nServed, int &totalWait, int &totalLength) {    Queue<int> queue;    int timeRemaining = 0;    nServed = 0;    totalWait = 0;    totalLength = 0;    for (int t = 0; t < SIMULATION_TIME; t++) {        if (randomChance(ARRIVAL_PROBABILITY)) {            queue.enqueue(t);        }        if (timeRemaining > 0) {            timeRemaining--;        } else if (!queue.isEmpty()) {            totalWait += t - queue.dequeue();            nServed++;            timeRemaining = randomInteger(MIN_SERVICE_TIME, MAX_SERVICE_TIME);        }        totalLength += queue.size();    }}void printReport(int nServed, int totalWait, int totalLength) {    cout << "Simulation results given the following constants:" << endl;    cout << fixed << setprecision(2);    cout << "SIMULATION TIME:   " << setw(4) << SIMULATION_TIME << endl;    cout << "Customers served: " << setw(4) << nServed << endl;    cout << "Average waiting time: " << setw(7) << double(totalWait) / nServed << endl;    cout << "Average queue length: " << setw(7) << double(totalLength) / SIMULATION_TIME << endl;}

输出：

Simulation results given the following constants:

SIMULATION TIME: 2000

Customers served: 103

Average waiting time: 5.60

Average queue length: 0.29

map介绍

A map is a generalization of this idea that provides an association between an identify tag called a key and an associated value, which may be a much larger and more complicated structure.

定义一个字典类

Map<string, string> dictionary;

key 和 value都是string类型。

读取文件操作

// This program looks up a three-letter airport code in a Map object.#include <iostream>#include <fstream>#include <string>#include "error.h"#include "map.h"#include "strlib.h"using namespace std;void readCodeFile(string filename, Map<string, string> &map);int main() {    Map<string, string> airportCodes;    readCodeFile("AirportCodes.txt", airportCodes);    while (true) {        string line;        cout << "Airport code: ";        getline(cin, line);        if (line == "") break;        string code = toUpperCase(line);        if (airportCodes.containsKey(code)) {            cout << code << " is in " << airportCodes.get(code) << endl;        } else {            cout << "There is no such airport code" << endl;        }    }    return 0;}void readCodeFile(string filename, Map<string, string> &map) {    ifstream infile;    infile.open(filename.c_str());    if (infile.fail()) error("Can't read the data file");    string line;    while (getline(infile,line)) {        if (line.length() < 4 || line[3] != '=') {            error("Illegal data line: " + line);        }        string code = toUpperCase(line.substr(0, 3));        map.put(code, line.substr(4));    }    infile.close();}

map[key] = value;