#include <iostream>
#include <string>
#include <string.h>

using std::cout;
using std::endl;

/**
 * Note: 增加了奇怪的知識(shí)點(diǎn):
 * 1. std::string 創(chuàng)建的每個(gè)對(duì)象，都會(huì)預(yù)留15個(gè)字節(jié)的空間；
 * 2. std::string(""), 預(yù)留了15個(gè)字節(jié)的空間;
 * (就像創(chuàng)建了一個(gè)空的倉(cāng)庫(kù)皮服，倉(cāng)庫(kù)里面沒(méi)放東西辛慰。但是, 如果其他人有倉(cāng)庫(kù)鑰匙的話其垄，依然可以使用這個(gè)倉(cāng)庫(kù))
 * 
 * str.capacity(): 返回當(dāng)前為字符串分配的存儲(chǔ)空間大小扔役，以字節(jié)表示权纤。
 *
 * data(): const char* data() const noexcept;
 * c_str(): const char* c_str() const noexcept;
 * Both string::data and string::c_str are synonyms and return the same value.
 * 官方解釋：data() 和 c_str() 是一樣的
 * 
 *
*/

int main() {

    // init empty string
    std::string str("");
    std::cout << "size: "       << str.size()       << endl;
    std::cout << "length: "     << str.length()     << endl;
    std::cout << "capacity: "   << str.capacity()   << endl;
    std::cout << "max_size: "   << str.max_size()   << endl;
    std::cout << "data: "       << str.data()       << endl;
    std::cout << "Address of str: " << &str << endl;

    char *mch = (char*)str.data();
    std::cout << "mch: " << mch << endl;
    std::cout << "Address of mch: " << static_cast<void *>(mch) << endl;

    char tem[5] = "q3we"; // '\0'

    memcpy((void*)(str.c_str()), tem, 5);
    std::cout << "size: "       << str.size()       << endl;
    std::cout << "length: "     << str.length()     << endl;
    std::cout << "capacity: "   << str.capacity()   << endl;
    std::cout << "max_size: "   << str.max_size()   << endl;
    std::cout << "data: "       << str.data()       << endl;
    std::cout << "Address of str: " << &str << endl;

    return 0;
}

結(jié)果：
size: 0
length: 0
capacity: 15
max_size: 9223372036854775807
data: 
Address of str: 0x7ffc76fa61f0
mch: 
Address of mch: 0x7ffc76fa6200
size: 0
length: 0
capacity: 15
max_size: 9223372036854775807
data: q3we
Address of str: 0x7ffc76fa61f0