std::string::erase in C++ 之 erase()方法截取string的前几位、后几位

Syntax 1: Erases all characters in a string 

string& string ::erase ()

// CPP code to illustrate
// erase() function
 
#include <iostream>
#include <string>
using namespace std;
 
// Function to demo erase()
void eraseDemo(string str)
{
    // Deletes all characters
    str.erase();
 
    cout << "After erase() : ";
    cout << str;
}
 
// Driver code
int main()
{
    string str("Hello World!");
 
    cout << "Before erase() : ";
    cout << str << endl;
    eraseDemo(str);
 
    return 0;
}

output:

Before erase() : Hello World!
After erase() : 

Syntax 2: Erases all characters after position ‘pos’ 

string& string ::erase (size_type pos)
- Throw out_of_range if idx > size().

// CPP code to illustrate working of
// erase(idx)

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

// Function to demo erase
void eraseDemo(string str)
{
    // Deletes all characters except first one
    str.erase(1);

    cout << "After erase(idx) : ";
    cout << str;
}

// Driver code
int main()
{
    string str("Hello World!");

    cout << "Before erase(idx) : ";
    cout << str << endl;
    eraseDemo(str);

    return 0;
}

output:

Before erase(idx) : Hello World!
After erase(idx) : H

Syntax 3: Erases at most, len characters of *this, starting at index idx. 

string& string ::erase (size_type idx, size_type len )
- If len is missing, all remaining characters are removed.
- Throw out_of_range if idx > size().
- 

// CPP code to illustrate
// erase(size_type idx, size_type len )
#include <iostream>
#include <string>
using namespace std;

// Function to demo erase
void eraseDemo(string str)
{
    // Deletes 4 characters from index number 1
    str.erase(1, 4);

    cout << "After erase : ";
    cout << str;
}

// Driver code
int main()
{
    string str("Hello World!");

    cout << "Before erase : ";
    cout << str << endl;
    eraseDemo(str);

    return 0;
}

output:

Before erase : Hello World!
After erase : H World!

Syntax 4: Erase the single character at iterator position pos. 

string& string ::erase (iterator pos)
- Return the first character after the last character removed
- If no such character is remaining then, returns 
  string::end() i.e. position after the last character.

// CPP code to illustrate
// erase(iterator pos)

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

// Function to demo erase
void eraseDemo(string str)
{
    // Deletes character at position 4
    str.erase(str.begin() + 4);

    cout << "After erase : ";
    cout << str;
}

// Driver code
int main()
{
    string str("Hello World!");

    cout << "Before erase : ";
    cout << str << endl;
    eraseDemo(str);

    return 0;
}

output:

Before erase : Hello World!
After erase : Hell World!

Syntax 5: Erase characters from iterator pos. to another iterator pos.

string& string ::erase (iterator beg, iterator end )
- Erases all characters of the range [ beg, end)
- Returns end i.e. the first character after the
  last character removed.
- If no such character is remaining then, returns 
  string::end() i.e. position after the last character

// CPP code to illustrate
// erase(iterator pos, iterator end)

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

// Function to demo erase
void eraseDemo(string str)
{
    // Deletes all characters between 0th index and
    // str.end() - 6
    str.erase(str.begin() + 0, str.end() - 6);

    cout << "After erase : ";
    cout << str;
}

// Driver code
int main()
{
    string str("Hello World!");

    cout << "Before erase : ";
    cout << str << endl;
    eraseDemo(str);

    return 0;
}

output:

Before erase : Hello World!
After erase : World!

 

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from:https://www.geeksforgeeks.org/stdstringerase-in-cpp/