How can I use erase() method of std::string? How can I erase part of a string in my C++ software? Here are the answers with C++ examples.
Generally, as an introduction to C++, in addition to int, float, double there is another data type called string that we use for alphanumeric variables. In C++ there are several typedefs for common character types are provided: String types are defined in header <string>.
Strings are the string class for byte characters represented with string and alphanumeric characters are stored and displayed in string forms. In another terms string stores for the alphanumeric text with 1 byte chars, called ASCII chars. Strings are the instantiation of the basic_string class template that uses char as the character type. Simply we can define a string as below,
|
1 2 3 |
std::string str = "This is a String"; |
String has methods to assign, copy, align, replace or to operate with other strings. These methods can be used in all string methods with their appropriate syntax. We can erase part of a string by using erase() method. Let’s see this method now.
How to remove part of a string with the C++ erase() method
erase() method of std::string in C++ removes string characters from the string in a given range. We can directly give the start position in a string to erase all behind as given Syntax below
|
1 2 3 |
basic_string& erase( size_type start_position); // Until C++20 |
or we can erase inside of a string by using start position to delete and number of characters. Thus, erase() method will delete all characters in this given Syntax below.
|
1 2 3 |
basic_string& erase( size_type start_position, size_type char_count); // Until C++20 |
Here is an erase() example that uses both erase() methods
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 |
#include <iostream> #include <string> int main() { std::string str; str = "This is my string in C++"; str.erase(4); std::cout << str << std::endl; str = "This is my string in C++"; str.erase(7, 13); std::cout << str << std::endl; getchar(); return 0; } |
and the output will be,
|
1 2 3 4 |
This This is C++ |
As you see in the first part we delete all after the 4th character and in the second part we delete 13 characters after 7th character,
Why do we get an “out of range” error when trying to use the C++ Erase() method?
As you can see in the example above, we can directly copy, assign, replace or insert any string after its some part being erased. When we use erase() method, we must be sure that the first parameter is lower than the string size (str.size()) and the second parameter is lower than size()-first_parameter, which means both should be inside the string. If the second parameter exceeds the string size, it returns remaining string till the position without throwing an exception. If the first parameter exceed the limits of string (size of string) then this erase method will throw out_of_range, we can catch this exception as given example below,
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 |
#include <iostream> #include <string> int main() { std::string str; str = "This is my string in C++"; try { str.erase( 64, 2); std::cout << str << std::endl; } catch(const std::out_of_range& e) { std::cout << "Out of range, please check string size\n"; } getchar(); return 0; } |
In this example above, we try to erase 2 characters of this given string starting from 64th character which means that we exceed the limits of this string size, and the output will be,
|
1 2 3 |
Out of range, please check string size |
As you see it is very easy to erase any part of a string, and this erase() method can be used with wstrings as given in the examples above.
