17.5节练习

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练习17.5.34 编写一个程序，展示如何使用表17.17和表17.18中的每个操作符。

#include <iostream>using namespace std;int main(){int val = 10;float val2 = 10.0;bool bool_val = val;cout << boolalpha << bool_val << noboolalpha << endl;cout << showbase << val << endl;cout << hex << val << endl;cout << oct << val << noshowbase << endl;cout << val2 << endl;cout << showpoint << val2 << noshowpoint << endl;cout << showpos << val << noshowpos << endl;//并没有显示+cout << uppercase << showbase << hex << 1212422424241 << nouppercase << noshowbase << endl;//...}

练习17.35 修改第670页中的程序，打印2的平方根，但这次打印十六进制数字的大写形式。

#include <iostream>#include <cmath>using namespace std;int main(){cout << uppercase << showbase << hexfloat << sqrt(2) << endl;cout << nouppercase << noshowbase;}

练习17.36 修改上一题中的程序，打印不同的浮点数，使它们排成一列。

#include <iostream>#include <cmath>#include <iomanip>using namespace std;int main(){cout << setw(12) << left << 100 << endl;cout << setw(12) << right << 100 << setfill(' ') << endl;cout << setw(12) << -3 << endl;cout << setw(12) << internal << -3 << endl;cout << setw(12) << setfill('*') << hexfloat << 15.0 << defaultfloat << endl;cout << setw(12) << 100 << endl;}

练习17.37 用未格式化版本的getline逐行读取一个文件。测试你的程序，给它一个文件，既包含空行又包含长度超过你传递给getline的字符数组大小的行。

#include <iostream>#include <fstream>#include <string>using namespace std;int main(){fstream in("17.37.txt");string line;while (getline(in, line)) {cout << line << endl;}in.close();cout << endl;fstream in2("17.37.txt");char ch[100];while (in2) {in2.getline(ch, 10);cout << ch << endl;}in2.close();}

练习17.38 扩展上一题中你的程序，将读入的每个单词打印到它所在的行。

#include <iostream>#include <fstream>#include <cstdio>using namespace std;int main(){fstream in("17.37.txt");char ch;while (in.get(ch)) {cout.put(ch);}cout << endl;}

练习17.39 对本节给出的seek程序，编写你自己的版本。

#include <iostream>#include <fstream>#include <cstdlib>#include <string>using namespace std;int main(){fstream inOut("17.39.txt", fstream::ate);if (inOut) {cerr << "Unable to open file!" << endl;return EXIT_FAILURE;}fstream::pos_type end_mark = inOut.tellg();inOut.seekg(0, fstream::beg);size_t cnt = 0;string line;while (inOut && inOut.tellg() != end_mark && getline(inOut, line)) {cnt += line.size() + 1;auto mark = inOut.tellg();inOut.seekp(0, fstream::end);inOut << cnt;if (mark != end_mark) {inOut << " ";}inOut.seekg(mark);}inOut.seekp(0, fstream::end);inOut << "\n";inOut.close();return 0;}

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