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C++ 將字符串值賦給CHAR數(shù)組的實現(xiàn)

更新時間：2021年01月13日 10:23:36 作者：dyz_123456

這篇文章主要介紹了C++ 將字符串值賦給CHAR數(shù)組的實現(xiàn)，具有很好的參考價值，希望對大家有所幫助。一起跟隨小編過來看看吧

我就廢話不多說啦，大家還是直接看代碼吧~

CHAR name[50];
strcpy(name, "tagname");

補充：將char* 賦值給std::string的一些陷阱

這段時間，總是要使用char或者char* 賦值給std::string，踩了不少坑。于是寫了個測試代碼，如果你不想看我的代碼，可以跳到下面直接看總結(jié)：

#include <string>
#include <iostream> 
using namespace std; 
int main(int argc, char* argv[])
{
  string str1;
  cout << "str1:" << str1 << " length: " << str1.length() << " size: " << str1.size() << " capacity: " << str1.capacity() << endl;
 
  string str2("hello");
  cout << "str2:" << str2 << " length: " << str2.length() << " size: " << str2.size() << " capacity: " << str2.capacity() << endl;
 
  string str3(4, 'A');
  cout << "str3:" << str3 << " length: " << str3.length() << " size: " << str3.size() << " capacity: " << str3.capacity() << endl;
 
  string str4(str2);
  cout << "str4:" << str4 << " length: " << str4.length() << " size: " << str4.size() << " capacity: " << str4.capacity() << endl;
 
  cout << "-----------------------------------------------" << endl;
 
  char sz1[10] = { 0 };
  sz1[0] = 'a';
  sz1[1] = 'b';
  sz1[2] = 'c';
  char sz2[10] = { 0 };
  sz2[0] = 'a';
  sz2[3] = 'b';
  sz2[4] = 'c';
 
  string str5(sz1);
  string str6(sz1, 2);
  string str71(sz1, 4);
  string str72(sz1, 10);
  string str73(sz1, 30);
 
  cout << "str5:" << str5 << " length: " << str5.length() << " size: " << str5.size() << " capacity: " << str5.capacity() << endl;
  cout << "str6:" << str6 <<" length: " << str6.length() << " size: " << str6.size() << " capacity: " << str6.capacity() << endl;
  cout << "str71:" << str71 << " length: " << str71.length() << " size: " << str71.size() << " capacity: " << str71.capacity() << endl;
  cout << "str72:" << str72 << " length: " << str72.length() << " size: " << str72.size() << " capacity: " << str72.capacity() << endl;
  cout << "str73:" << str73 << " length: " << str73.length() << " size: " << str73.size() << " capacity: " << str73.capacity() << endl;
 
  cout << "-----------------------------------------------" << endl;
 
  string str8(sz2);
  string str9(sz2, 1);
  string str10(sz2, 2);
  string str11(sz2, 4);
  string str12(sz2, 10);
 
  cout << "str8:" << str8 <<" length: " << str8.length() << " size: " << str8.size() << " capacity: " << str8.capacity() << endl;
  cout << "str9:" << str9 << " length: " << str9.length() << " size: " << str9.size() << " capacity: " << str9.capacity() << endl;
  cout << "str10:" << str10 << " length: " << str10.length() << " size: " << str10.size() << " capacity: " << str10.capacity() << endl;
  cout << "str11:" << str11 << " length: " << str11.length() << " size: " << str11.size() << " capacity: " << str11.capacity() << endl;
  cout << "str12:" << str12 << " length: " << str12.length() << " size: " << str12.size() << " capacity: " << str12.capacity() << endl;
 
  cout << "-----------------------------------------------" << endl;
 
  string str13 = sz1;
  string str14 = sz2;
  cout << "str13:" << str13 << " length: " << str13.length() << " size: " << str13.size() << " capacity: " << str13.capacity() << endl;
  cout << "str14:" << str14 << " length: " << str14.length() << " size: " << str14.size() << " capacity: " << str14.capacity() << endl;
 
  cout << "-----------------------------------------------" << endl;
 
  string str15;
  str15.append(sz1);
  string str16;
  str16.append(sz1, 2);
  cout << "str15:" << str15 << " length: " << str15.length() << " size: " << str15.size() << " capacity: " << str15.capacity() << endl;
  cout << "str16:" << str16 << " length: " << str16.length() << " size: " << str16.size() << " capacity: " << str16.capacity() << endl;
 
  cout << "-----------------------------------------------" << endl;
 
  string str17;
  str17.append(sz2);
  string str18;
  str18.append(sz2, 3);
  string str19;
  str19.append(sz2, 10);
  cout << "str17:" << str17 << " length: " << str17.length() << " size: " << str17.size() << " capacity: " << str17.capacity() << endl;
  cout << "str18:" << str18 << " length: " << str18.length() << " size: " << str18.size() << " capacity: " << str18.capacity() << endl;
  cout << "str19:" << str19 << " length: " << str19.length() << " size: " << str19.size() << " capacity: " << str19.capacity() << endl;
 
  cout << "-----------------------------------------------" << endl;
 
  string str20;
  str20 += sz1;
  string str21;
  str21 += sz2;
  cout << "str20:" << str20 << " length: " << str20.length() << " size: " << str20.size() << " capacity: " << str20.capacity() << endl;
  cout << "str21:" << str21 << " length: " << str21.length() << " size: " << str21.size() << " capacity: " << str21.capacity() << endl;
 
  cout << "-----------------------------------------------" << endl;
 
  string str22;
  str22.assign(sz1);
  string str23;
  str23.assign(sz1, 9);
  string str24;
  str24.assign(sz1, 15);
  cout << "str22:" << str22 << " length: " << str22.length() << " size: " << str22.size() << " capacity: " << str22.capacity() << endl;
  cout << "str23:" << str23 << " length: " << str23.length() << " size: " << str23.size() << " capacity: " << str23.capacity() << endl;
  cout << "str24:" << str24 << " length: " << str24.length() << " size: " << str24.size() << " capacity: " << str24.capacity() << endl;
 
  cout << "-----------------------------------------------" << endl;
 
  string str25;
  str25.assign(sz2);
  string str26;
  str26.assign(sz2, 4);
  string str27;
  str27.assign(sz1, 15);
  cout << "str25:" << str25 << " length: " << str25.length() << " size: " << str25.size() << " capacity: " << str25.capacity() << endl;
  cout << "str26:" << str26 << " length: " << str26.length() << " size: " << str26.size() << " capacity: " << str26.capacity() << endl;
  cout << "str27:" << str27 << " length: " << str27.length() << " size: " << str27.size() << " capacity: " << str27.capacity() << endl;
 
  cout << "-----------------------------------------------" << endl;
 
  printf("%s\n", str26.c_str());
  printf("%s\n", str26.data());
 
  
  return 0;
}

輸出結(jié)果是：

現(xiàn)總結(jié)如下：

1. 將char*賦值給std::string如果不指定長度，則會默認以\0截斷（ASCII碼值為0）；如果指定的長度超過char*字符串的長度，用std::cout系列的函數(shù)輸出時，會把不屬于該char*之后的內(nèi)存值打印出來。而對于printf系列的函數(shù)來打印std::string時遇到\0也會截斷，因而不能完全顯示。這點在打印或輸出到日志時，這類字符串時需要特別注意。

2. 如果是單個字符和一個字符串賦值給std::string寫法是有區(qū)別的 —— 對于char，數(shù)目是第一個參數(shù)，對于char* 數(shù)目是第二個參數(shù)。

例如，假定ptsr是一個字符串或者字符。如果pstr是一個字符串，那么要寫成string(pstr, n)，如果pstr是一個字符，那么要寫成string(n, pstr)，而此時string(pstr, n)是一個錯誤的寫法，可能會導(dǎo)致你的程序產(chǎn)生莫名其妙的問題，因為如果pstr是一個負值，負數(shù)轉(zhuǎn)換成無符號整數(shù)size_t類型，n將非常大，會導(dǎo)致構(gòu)造字符串時length非常大導(dǎo)致std::string構(gòu)造時拋出異常?？催@兩種初始化的構(gòu)造函數(shù)簽名：

string (const char* s, size_t n);
string(size_t n, char c);

請注意這個區(qū)別??！特別容易想當(dāng)然地寫錯。如果pstr對應(yīng)數(shù)值比較小的正數(shù)，可能不會產(chǎn)生異常，但其實程序狀態(tài)也不是你想要的。如果是負數(shù)，程序?qū)⒅苯赢a(chǎn)生異常。拋出：std::length_error 。所以出現(xiàn)這個異常信息，你就要好好檢查下你初始化std::string的長度信息了。

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