C++中string和char[]类型的区别 [英] Difference between string and char[] types in C++

问题描述

我知道一点 C，现在我正在研究 C++.我习惯于使用字符数组来处理 C 字符串，但是当我查看 C++ 代码时，我看到有使用字符串类型和字符数组的示例:

I know a little C and now I'm taking a look at C++. I'm used to char arrays for dealing with C strings, but while I look at C++ code I see there are examples using both string type and char arrays:

#include <iostream>
#include <string>
using namespace std;

int main () {
  string mystr;
  cout << "What's your name? ";
  getline (cin, mystr);
  cout << "Hello " << mystr << ".
";
  cout << "What is your favorite team? ";
  getline (cin, mystr);
  cout << "I like " << mystr << " too!
";
  return 0;
}

和

#include <iostream>
using namespace std;

int main () {
  char name[256], title[256];

  cout << "Enter your name: ";
  cin.getline (name,256);

  cout << "Enter your favourite movie: ";
  cin.getline (title,256);

  cout << name << "'s favourite movie is " << title;

  return 0;
}

(两个例子都来自 http://www.cplusplus.com)

我想这是一个被广泛询问和回答(显而易见?)的问题，但如果有人能告诉我在 C++ 中处理字符串的两种方式(性能、API 集成、方式)之间的确切区别，那就太好了每一个都更好，...)

I suppose this is a widely asked and answered (obvious?) question, but it would be nice if someone could tell me what's exactly the difference between that two ways for dealing with strings in C++ (performance, API integration, the way each one is better, ...).

谢谢.

推荐答案

char 数组就是这样 - 一个字符数组:

A char array is just that - an array of characters:

• 如果在堆栈上分配(如您的示例中)，它将始终占用例如.256 字节，无论它包含多长的文本
• 如果在堆上分配(使用 malloc() 或 new char[])，您负责之后释放内存，并且您将始终拥有堆分配的开销.
• 如果将超过 256 个字符的文本复制到数组中，它可能会崩溃、产生丑陋的断言消息或导致程序中其他地方出现无法解释的(错误)行为.
• 要确定文本的长度，必须逐个字符地扫描数组以获得 字符.

字符串是一个包含字符数组的类，但会自动为您管理它.大多数字符串实现都有一个由 16 个字符组成的内置数组(因此短字符串不会对堆造成碎片)，并将堆用于更长的字符串.

A string is a class that contains a char array, but automatically manages it for you. Most string implementations have a built-in array of 16 characters (so short strings don't fragment the heap) and use the heap for longer strings.

您可以像这样访问字符串的字符数组:

You can access a string's char array like this:

std::string myString = "Hello World";
const char *myStringChars = myString.c_str();

C++ 字符串可以包含嵌入的 字符，无需计算即可知道它们的长度，对于短文本比堆分配的字符数组更快，并保护您免受缓冲区溢出的影响.此外，它们更具可读性和易用性.

C++ strings can contain embedded characters, know their length without counting, are faster than heap-allocated char arrays for short texts and protect you from buffer overruns. Plus they're more readable and easier to use.

然而，C++ 字符串并不(非常)适合跨 DLL 边界使用，因为这将要求此类 DLL 函数的任何用户确保他使用完全相同的编译器和 C++ 运行时实现，以免他的字符串类冒险表现不同.

However, C++ strings are not (very) suitable for usage across DLL boundaries, because this would require any user of such a DLL function to make sure he's using the exact same compiler and C++ runtime implementation, lest he risk his string class behaving differently.

通常，字符串类也会在调用堆上释放其堆内存，因此如果您使用的是运行时的共享(.dll 或 .so)版本，它只能再次释放内存.

Normally, a string class would also release its heap memory on the calling heap, so it will only be able to free memory again if you're using a shared (.dll or .so) version of the runtime.

简而言之:在所有内部函数和方法中使用 C++ 字符串.如果您曾经编写过 .dll 或 .so，请在您的公共(dll/so-exposed)函数中使用 C 字符串.

In short: use C++ strings in all your internal functions and methods. If you ever write a .dll or .so, use C strings in your public (dll/so-exposed) functions.

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