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Ruby @Sprout 2022

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Ruby @Sprout 2022

人(´・ω・)ﾉ 今日主題 ヽ(・ε・*)人

Ruby @Sprout 2022

ω・)ﾉ 今日主題 ヽ(・ε

Ruby @Sprout 2022

)ﾉ 今日主題 ヽ(

Ruby @Sprout 2022

今日主題

Ruby @Sprout 2022

C++ String & FileIO

Ruby @Sprout 2022

Outline

C-string Review

std::string

Applications of std::string

std::stringstream

FileIO

Applications of FileIO

C-string Review

std::string

Applications of std::string

std::stringstream

FileIO

Applications of FileIO

C-string 的本質

C-string 本質上是 char 陣列

C-string Review 1

C-string 的操基本操作

利用 <cstring> (<string.h>) 中的函式

C-string Review 2

字面常數字串存在哪裡？

是 Stack 嗎？還是 Heap 呢？答案是：都不是！

C-string Review 3-1

C-string Review 3-2

多數 Bug 的根源–未定義行為

因為 C-string 本質是陣列，所以如同其他型態的陣列一樣，超出範圍不一定會報錯，是未定義行為！

C-string Review 4

C-string Review

std::string

Applications of std::string

std::stringstream

FileIO

Applications of FileIO

A peek into std::string

C++ String 1
C++ String 2

各種「附帶功能」(Methods)

C++ String 3

各種「附帶功能」(Methods)

更多、更詳細的說明文件 (Documentation) 請參考

C++ reference

Any questions?

C-string Review

std::string

Applications of std::string

std::stringstream

FileIO

Applications of FileIO

課堂練習 1

Sprout OJ No. 441

Solution

哈哈不給你看，上課講解！

Any questions?

C-string Review

std::string

Applications of std::string

std::stringstream

FileIO

Applications of FileIO

What is "stream"

Stream ，即「流」。

• 輸入流：字節從設備流向內存
• 輸出流：字節從內存流向設備

Reference

ostream

• cout
• cerr
• clog

istream

• cin

Sample code

w/o stringstream
w/ stringstram

課堂練習 2

Sprout OJ No. 442

C-string Review

std::string

Applications of std::string

std::stringstream

FileIO

Applications of FileIO

Create (Overwrite) a file

#include <iostream>
#include <fstream>
using namespace std;

int main() {
    ofstream outFile;
    outFile.open("out.txt");
    outFile << "Some text";
    outFile.close();
    return 0;
}

Load an existing file

#include <iostream>
#include <fstream>
#include <string>
using namespace std;

int main() {
    ifstream inFile;
    inFile.open("in.txt");
    string s; 
    while (inFile >> s) cout << s << endl;
    inFile.close();
    return 0;
}

Load and overwrite an existing file

#include <bits/stdc++.h>
using namespace std;
const string FILENAME = "last_login_time.txt";

int main() {
    ifstream inFile; ofstream outFile;
    inFile.open(FILENAME);
    time_t curr = time(nullptr), last; inFile >> last;
    inFile.close();
    cout << "It has been " << curr-last << " seconds since your last login." << endl;
    outFile.open(FILENAME);
    outFile << curr;
    outFile.close();
    return 0;
}

C-string Review

std::string

Applications of std::string

std::stringstream

FileIO

Applications of FileIO

Loading testcases

#include <bits/stdc++.h>
using namespace std;

int main() {
    ifstream inFile("testcase.txt");
    int n, _max = -1;
    while (inFile >> n)
        _max = max(n, _max);
    cout << "The max numbers out of all numbers in the testcase: " << _max << endl;
    inFile.close();
    return 0;
}

Quick Review

• C-string vs. C++ string
• stream
• stringstream
• FileIO

感謝參與！