The C++ string

The C++ string

C-style string

C-style strings originate in the C language and continue to be supported in C. T he string is actually an array of one-dimensional characters terminated with the null character ''. Therefore, a string that ends with null contains the characters that make up the string.

The following declaration and initialization create a "Hello" string. B ecause empty characters are stored at the end of the array, the character array is one more size than the number of characters in the word "Hello". '};

Depending on the array initialization rules, you can write the above statement as follows:

char greeting[] = "Hello";

Here is the memory representing the string defined in C/C?

In fact, you don't need to put the null character at the end of the string constant. W hen you initialize an array, the compiler automatically places '' at the end of the string. Let's try to output the string above

#include <iostream>

using namespace std;

int main ()
{
   char greeting[6] = {'H', 'e', 'l', 'l', 'o', '\0'};

   cout << "Greeting message: ";
   cout << greeting << endl;

   return 0;
} 

When the above code is compiled and executed, it produces the following results:

Greeting message: Hello

There are a large number of functions in C++to manipulate strings ending in null: supports a wide range of functions that manipulate null-terminated strings:

The following example uses some of the above functions:

#include <iostream>
#include <cstring>

using namespace std;

int main ()
{
   char str1[11] = "Hello";
   char str2[11] = "World";
   char str3[11];
   int  len ;

   // 复制 str1 到 str3
   strcpy( str3, str1);
   cout << "strcpy( str3, str1) : " << str3 << endl;

   // 连接 str1 和 str2
   strcat( str1, str2);
   cout << "strcat( str1, str2): " << str1 << endl;

   // 连接后，str1 的总长度
   len = strlen(str1);
   cout << "strlen(str1) : " << len << endl;

   return 0;
}

When the above code is compiled and executed, it produces the following results:

strcpy( str3, str1) : Hello
strcat( str1, str2): HelloWorld
strlen(str1) : 10

The String class in C+

The C++ standard library provides a string class type that supports all of the above operations, plus additional features. Now that we're going to learn about this class in the standard library, let's take a look at the following example:

You may not yet be able to fully understand this example, because so far we haven't discussed classes and objects. So now you can just take a cursive look at the instance and wait until you understand the object-oriented concept before you look back to understand it.

#include <iostream>
#include <string>

using namespace std;

int main ()
{
   string str1 = "Hello";
   string str2 = "World";
   string str3;
   int  len ;

   // 复制 str1 到 str3
   str3 = str1;
   cout << "str3 : " << str3 << endl;

   // 连接 str1 和 str2
   str3 = str1 + str2;
   cout << "str1 + str2 : " << str3 << endl;

   // 连接后，str3 的总长度
   len = str3.size();
   cout << "str3.size() :  " << len << endl;

   return 0;
} 

When the above code is compiled and executed, it produces the following results:

str3 : Hello
str1 + str2 : HelloWorld
str3.size() :  10