查看“C++ string”的源代码

===int转string===
 std::string str = std::to_string(num);


===string比较===
 str1.compare(str2);


===basic_string::find===
向前搜索字符串，搜索与指定字符序列匹配的第一个子字符串。


<pre>
// basic_string_find.cpp
// compile with: /EHsc
#include <string>
#include <iostream>

int main( )
{
   using namespace std;

   // The first member function
   // searches for a single character in a string
   string str1 ( "Hello Everyone" );
   cout << "The original string str1 is: " << str1 << endl;
   basic_string <char>::size_type indexCh1a, indexCh1b;

   indexCh1a = str1.find ( "e" , 3 );
   if (indexCh1a != string::npos )
      cout << "The index of the 1st 'e' found after the 3rd"
           << " position in str1 is: " << indexCh1a << endl;
   else
      cout << "The character 'e' was not found in str1 ." << endl;

   indexCh1b = str1.find ( "x" );
   if (indexCh1b != string::npos )
      cout << "The index of the 'x' found in str1 is: "
           << indexCh1b << endl << endl;
   else
      cout << "The Character 'x' was not found in str1."
           << endl << endl;

   // The second member function searches a string
   // for a substring as specified by a C-string
   string str2 ( "Let me make this perfectly clear." );
   cout << "The original string str2 is: " << str2 << endl;
   basic_string <char>::size_type indexCh2a, indexCh2b;

   const char *cstr2 = "perfect";
   indexCh2a = str2.find ( cstr2 , 5 );
   if ( indexCh2a != string::npos )
      cout << "The index of the 1st element of 'perfect' "
           << "after\n the 5th position in str2 is: "
           << indexCh2a << endl;
   else
      cout << "The substring 'perfect' was not found in str2 ."
           << endl;

   const char *cstr2b = "imperfectly";
   indexCh2b = str2.find ( cstr2b , 0 );
   if (indexCh2b != string::npos )
      cout << "The index of the 1st element of 'imperfect' "
           << "after\n the 5th position in str3 is: "
           << indexCh2b << endl;
   else
      cout << "The substring 'imperfect' was not found in str2 ."
           << endl << endl;

   // The third member function searches a string
   // for a substring as specified by a C-string
   string str3 ( "This is a sample string for this program" );
   cout << "The original string str3 is: " << str3 << endl;
   basic_string <char>::size_type indexCh3a, indexCh3b;

   const char *cstr3a = "sample";
   indexCh3a = str3.find ( cstr3a );
   if ( indexCh3a != string::npos )
      cout << "The index of the 1st element of sample "
           << "in str3 is: " << indexCh3a << endl;
   else
      cout << "The substring 'sample' was not found in str3 ."
           << endl;

   const char *cstr3b = "for";
   indexCh3b = str3.find ( cstr3b , indexCh3a + 1 , 2 );
   if (indexCh3b != string::npos )
      cout << "The index of the next occurrence of 'for' is in "
           << "str3 begins at: " << indexCh3b << endl << endl;
   else
      cout << "There is no next occurrence of 'for' in str3 ."
           << endl << endl;

   // The fourth member function searches a string
   // for a substring as specified by a string
   string str4 ( "clearly this perfectly unclear." );
   cout << "The original string str4 is: " << str4 << endl;
   basic_string <char>::size_type indexCh4a, indexCh4b;

   string str4a ( "clear" );
   indexCh4a = str4.find ( str4a , 5 );
   if ( indexCh4a != string::npos )
      cout << "The index of the 1st element of 'clear' "
           << "after\n the 5th position in str4 is: "
           << indexCh4a << endl;
   else
      cout << "The substring 'clear' was not found in str4 ."
           << endl;

   string str4b ( "clear" );
   indexCh4b = str4.find ( str4b );
   if (indexCh4b != string::npos )
      cout << "The index of the 1st element of 'clear' "
           << "in str4 is: "
           << indexCh4b << endl;
   else
      cout << "The substring 'clear' was not found in str4 ."
           << endl << endl;
}
</pre>


<pre>
The original string str1 is: Hello Everyone
The index of the 1st 'e' found after the 3rd position in str1 is: 8
The Character 'x' was not found in str1.

The original string str2 is: Let me make this perfectly clear.
The index of the 1st element of 'perfect' after
the 5th position in str2 is: 17
The substring 'imperfect' was not found in str2 .

The original string str3 is: This is a sample string for this program
The index of the 1st element of sample in str3 is: 10
The index of the next occurrence of 'for' is in str3 begins at: 24

The original string str4 is: clearly this perfectly unclear.
The index of the 1st element of 'clear' after
the 5th position in str4 is: 25
The index of the 1st element of 'clear' in str4 is: 0
</pre>


===basic_string::length===
===basic_string::size===
返回字符串中元素的当前数目。

<pre>
// basic_string_length.cpp
// compile with: /EHsc
#include <string>
#include <iostream>

int main( )
{
   using namespace std;
   string str1 ("Hello world");
   cout << "The original string str1 is: " << str1 << endl;

   // The size and length member functions differ in name only
   basic_string <char>::size_type sizeStr1, lenStr1;
   sizeStr1 = str1.size ( );
   lenStr1 = str1.length ( );

   basic_string <char>::size_type capStr1, max_sizeStr1;
   capStr1 = str1.capacity ( );
   max_sizeStr1 = str1.max_size ( );

   // Compare size, length, capacity & max_size of a string
   cout << "The current size of original string str1 is: "
        << sizeStr1 << "." << endl;
   cout << "The current length of original string str1 is: "
        << lenStr1 << "." << endl;
   cout << "The capacity of original string str1 is: "
        << capStr1 << "." << endl;
   cout << "The max_size of original string str1 is: "
        << max_sizeStr1 << "." << endl << endl;

   str1.erase ( 6, 5 );
   cout << "The modified string str1 is: " << str1 << endl;

   sizeStr1 = str1.size ( );
   lenStr1 = str1.length ( );
   capStr1 = str1.capacity ( );
   max_sizeStr1 = str1.max_size ( );

   // Compare size, length, capacity & max_size of a string
   // after erasing part of the original string
   cout << "The current size of modified string str1 is: "
        << sizeStr1 << "." << endl;
   cout << "The current length of modified string str1 is: "
        << lenStr1 << "." << endl;
   cout << "The capacity of modified string str1 is: "
        << capStr1 << "." << endl;
   cout << "The max_size of modified string str1 is: "
        << max_sizeStr1 << "." << endl;
}
</pre>


===basic_string::substr===
从字符串起始处的指定位置复制最多某个数目的字符的子字符串。
<pre>
#include <string>
#include <iostream>

int main()
{
    using namespace std;

    string  str1("Heterological paradoxes are persistent.");
    cout << "The original string str1 is: \n " << str1
        << endl << endl;

    basic_string <char> str2 = str1.substr(6, 7);
    cout << "The substring str1 copied is: " << str2
        << endl << endl;

    basic_string <char> str3 = str1.substr();
    cout << "The default substring str3 is: \n " << str3
        << "\n which is the entire original string." << endl;
}
</pre>


<pre>
The original string str1 is:
Heterological paradoxes are persistent.

The substring str1 copied is: logical

The default substring str3 is:
Heterological paradoxes are persistent.
which is the entire original string.
</pre>


===basic_string::clear===
清除字符串中的全部元素。

<pre>
#include <string>
#include <iostream>

int main()
{
    using namespace std;
    string  str1("Hello world"), str2;
    basic_string <char>::iterator str_Iter;
    cout << "The original string str1 is: ";
    for (str_Iter = str1.begin(); str_Iter != str1.end(); str_Iter++)
        cout << *str_Iter;
    cout << endl;

    str1.clear();
    cout << "The modified string str1 is: ";
    for (str_Iter = str1.begin(); str_Iter != str1.end(); str_Iter++)
        cout << *str_Iter;
    cout << endl;

    //For an empty string, begin is equivalent to end
    if (str1.begin() == str1.end())
        cout << "Nothing printed above because "
        << "the string str1 is empty." << endl;
    else
        cout << "The string str1 is not empty." << endl;
}
</pre>


<pre>
The original string str1 is: Hello world
The modified string str1 is:
Nothing printed above because the string str1 is empty.
</pre>


===basic_string::erase===
从字符串中的指定位置删除一个或一系列元素。

<pre>
#include <string>
#include <iostream>

int main()
{
    using namespace std;

    // The 1st member function using a range demarcated
    // by iterators
    string str1("Hello world");
    basic_string <char>::iterator str1_Iter;
    cout << "The original string object str1 is: "
        << str1 << "." << endl;
    str1_Iter = str1.erase(str1.begin() + 3, str1.end() - 1);
    cout << "The first element after those removed is: "
        << *str1_Iter << "." << endl;
    cout << "The modified string object str1 is: " << str1
        << "." << endl << endl;

    // The 2nd member function erasing a char pointed to
    // by an iterator
    string str2("Hello World");
    basic_string <char>::iterator str2_Iter;
    cout << "The original string object str2 is: " << str2
        << "." << endl;
    str2_Iter = str2.erase(str2.begin() + 5);
    cout << "The first element after those removed is: "
        << *str2_Iter << "." << endl;
    cout << "The modified string object str2 is: " << str2
        << "." << endl << endl;

    // The 3rd member function erasing a number of chars
    // after a char
    string str3("Hello computer"), str3m;
    basic_string <char>::iterator str3_Iter;
    cout << "The original string object str3 is: "
        << str3 << "." << endl;
    str3m = str3.erase(6, 8);
    cout << "The modified string object str3m is: "
        << str3m << "." << endl;
}
</pre>


<pre>
The original string object str1 is: Hello world.
The first element after those removed is: d.
The modified string object str1 is: Held.

The original string object str2 is: Hello World.
The first element after those removed is: W.
The modified string object str2 is: HelloWorld.

The original string object str3 is: Hello computer.
The modified string object str3m is: Hello .
</pre>


==<string> 函数==

#getline
#stod
#stof
#stoi
#stol
#stold
#stoll
#stoul
#stoull
#swap
#to_string
#to_wstring


===getline===
将字符串从输入流中一行一行地提取出来。

以下代码演示两种模式下的 getline()：第一种使用默认分隔符（换行），第二种使用空格作为分隔符。 文件尾字符（键盘上的 CTRL-Z）用于控制 while 循环的终止。 此值会将 cin 的内部状态标志设置为 eofbit，后者必须使用 basic_ios::clear() 进行消除，这样第二个 while 循环才能正确运行。

<pre>
// compile with: /EHsc /W4
#include <string>
#include <iostream>
#include <vector>

using namespace std;

int main()
{
    string str;
    vector<string> v1;
    cout << "Enter a sentence, press ENTER between sentences. (Ctrl-Z to stop): " << endl;
    // Loop until end-of-file (Ctrl-Z) is input, store each sentence in a vector.
    // Default delimiter is the newline character.
    while (getline(cin, str)) {
        v1.push_back(str);
    }

    cout << "The following input was stored with newline delimiter:" << endl;
    for (const auto& p : v1) {
        cout << p << endl;
    }

    cin.clear();

    vector<string> v2;
    // Now try it with a whitespace delimiter
    while (getline(cin, str, ' ')) {
        v2.push_back(str);
    }

    cout << "The following input was stored with whitespace as delimiter:" << endl;
    for (const auto& p : v2) {
        cout << p << endl;
    }
}
</pre>