c++ primer 学习笔记11--动态内存

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书本411页。练习12.6：编写函数，返回一个动态分配的int的vector。将此vector传递给另一个函数，这个函数读取标准输入，将输入的值保存在vector元素中，再将vector传递给另一个函数，打印输入的值。记得在恰当的时候delete vector。

#include <iostream>  #include <vector>using namespace std;vector<int> *new_vector(void){return new(nothrow) vector<int>;}void read_ints(vector<int> *pv){int v;while (cin >> v){pv->push_back(v);}}void print_ints(vector<int> *pv){for (const auto &v : *pv)cout << v << " ";cout << endl;}int main(int argc, char *argv[]){vector<int> *pv = new_vector();if (!pv){cout << "内存不足" << endl;return -1;}read_ints(pv);print_ints(pv);delete pv;pv = nullptr;}

12.7使用shared_ptr。非内置指针

#include <iostream>  #include <vector>#include <memory>using namespace std;shared_ptr<vector<int>> new_vector(void){return make_shared<vector<int>>();}void read_ints(shared_ptr<vector<int>> spv){int v;while (cin >> v){spv->push_back(v);}}void print_ints(shared_ptr<vector<int>> spv){for (const auto & c : *spv){cout << c << " ";}cout << endl;}int main(int argc, char *argv[]){auto spv = new_vector();read_ints(spv);print_ints(spv);return 0;}

12.23连接两个字符串字面常量，将结果保存在一个动态的分配char数组中。

#include <iostream>  #include <cstring>using namespace std;int main(int argc, char *argv[]){const char*c1 = "Hello ";const char*c2 = "World";char *r = new char[strlen(c1) + strlen(c2) + 1];strcpy(r, c1);//拷贝strcat(r, c2);//链接cout << r << endl;string s1 = "Hello ";string s2 = "World";strcpy(r, (s1 + s2).c_str());cout << r << endl;delete[]r;return 0;}

12.24从标准输入中读取一个字符串，存入一个动态分配的字符数组中。描述你的程序如何处理变长输入

#include <iostream>  #include <cstring>using namespace std;int main(int argc, char *argv[]){char c;char *r = new char[20];int l = 0;while (cin.get(c)){if (isspace(c))break;r[l++] = c;if (l == 20){cout << "容量大于上限" << endl;break;}}r[l] = 0;cout << r << endl;delete[]r;return 0;}

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