std::string的resize()與reserve()的區別:

resize()：改變的是size()與capacity()的大小

(1)、比原來的變小之后，后面的會被截斷

(2)、比原來的變大之后，后面的會被填充新的東西，不同的編譯器可能會不同

reserve()：改變的只是capacity()的大小

程序如下：

#include <math.h> #include <stdio.h> #include <string> #include<iostream>using namespace std;int main() {std::string s1("hello");std::cout << "s1=" << s1 << " s1.size=" << s1.size() << " s1.capacity=" << s1.capacity() << endl;std::cout << "after resize to 2" << endl;s1.resize(2); //尺寸由5改變為2，多余字符被截掉了,只剩下hestd::cout << "s1=" << s1 << " s1.size=" << s1.size() << " s1.capacity=" << s1.capacity() << endl;std::cout << "after resize to 100" << endl;s1.resize(100);//尺寸由2改變為100,后面的數據被填充了98個astd::cout << "s1=" << s1 << " s1.size=" << s1.size() << " s1.capacity=" << s1.capacity() << endl;std::cout << "\n";std::cout << "===================================================================" << endl;std::cout << "\n";std::string s2("hello");std::cout << "s2=" << s2 << " s2.size=" << s2.size() << " s2.capacity=" << s2.capacity() << endl;std::cout << "after reserve to 20" << endl;s2.reserve(20); //只改變capacity()的大小，其他的不變std::cout << "s2=" << s2 << " s2.size=" << s2.size() << " s2.capacity=" << s2.capacity() << endl;std::cout << "after reserve to 2" << endl;s2.reserve(2); //只改變capacity()的大小，其他的不變std::cout << "s2=" << s2 << " s2.size=" << s2.size() << " s2.capacity=" << s2.capacity() << endl;return 0; }

結果：

總結

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