In C++, std::substr() is a predefined function used for string handling. string.h is the header file required for string functions. The substring function is used for handling string operations like strcat(), append(), etc. It generates a new string with its value initialized to a copy of a sub-string of this object.
This function takes two values pos and len as an argument and returns a newly constructed string object with its value initialized to a copy of a sub-string of this object. Copying of string starts from pos and is done till pos+len means [pos, pos+len).
Tóm Tắt
Important points:
- The index of the first character is 0 (not 1).
- If pos is equal to the string length, the function returns an empty string.
- If pos is greater than the string length, it throws out_of_range. If this happens, there are no changes in the string.
- If the requested sub-string len is greater than the size of a string, then returned sub-string is [pos, size()).
- If len is not passed as a parameter, then returned sub-string is [pos, size()).
Syntax:
string substr (size_t pos, size_t len) const;
Parameters:
- pos: Position of the first character to be copied.
- len: Length of the sub-string.
- size_t: It is an unsigned integral type.
Return value:
It returns a string object.
Example:
CPP
#include <string.h>
#include <iostream>
using namespace std;
int main()
{
string s1 = "Geeks";
string r = s1.substr(3, 2);
cout << "String is: " << r;
return 0;
}
Output
String is: ks
Time complexity: O(n)
Auxiliary Space: O(n)
Applications:
1. How to get a sub-string after a character?
In this, a string and a character are given and you have to print the sub-string followed by the given character.
Extract everything after the “:” in the string “dog:cat“.
Example:
C++
#include <string.h>
#include <iostream>
using namespace std;
int main()
{
string s = "dog:cat";
int pos = s.find(":");
string sub = s.substr(pos + 1);
cout << "String is: " << sub;
return 0;
}
Output
String is: cat
Time complexity: O(n)
Auxiliary Space: O(n)
2. How to get a sub-string before a character?
In this, a string and a character are given and you have to print the sub-string followed by the given character.
Extract everything before the “:” in the string “dog:cat“.
Example:
CPP
#include <string.h>
#include <iostream>
using namespace std;
int main()
{
string s = "dog:cat";
int pos = s.find(":");
string sub = s.substr(0 , pos);
cout << "String is: " << sub;
return 0;
}
Output
String is: dog
Time complexity: O(n)
Auxiliary Space: O(n)
3. Print all substrings of a given string
Given a string as an input. We need to write a program that will print all non-empty substrings of that given string.
Example:
C++
#include <bits/stdc++.h>
using namespace std;
void subString(string s, int n)
{
for (int i = 0; i < n; i++)
for (int len = 1; len <= n - i; len++)
cout << s.substr(i, len) << endl;
}
int main()
{
string s = "abcd";
subString(s, s.length());
return 0;
}
Output
a ab abc abcd b bc bcd c cd d
Time complexity: O( n3 )
Auxiliary Space: O(1)
4. Sum of all substrings of a string representing a number
Given an integer represented as a string, we need to get the sum of all possible substrings of this string.
Example:
C++
#include <bits/stdc++.h>
using namespace std;
int toDigit(char ch)
{
return (ch - '0');
}
int sumOfSubstrings(string num)
{
int n = num.length();
int sumofdigit[n];
sumofdigit[0] = toDigit(num[0]);
int res = sumofdigit[0];
for (int i = 1; i < n; i++) {
int numi = toDigit(num[i]);
sumofdigit[i] = (i + 1) * numi + 10 * sumofdigit[i - 1];
res += sumofdigit[i];
}
return res;
}
int main()
{
string num = "1234";
cout << sumOfSubstrings(num) << endl;
return 0;
}
Output
1670
Time Complexity: O(n)
Auxiliary Space: O(n)
5: Maximum value of all substrings of a string representing a number.
Given an integer represented as a string, we need to get the maximum of all possible substrings of the given string which is representing a number.
Example:
C++
#include <bits/stdc++.h>
using namespace std;
void subString(string s, int n)
{
vector<int> v;
for (int i = 0; i < n; i++){
for (int len = 1; len <= n - i; len++){
string sub =(s.substr(i, len));
int x=stoi(sub);
v.push_back(x);
}
}
cout<<*max_element(v.begin(),v.end())<<endl;
}
int main()
{
string s = "823";
subString(s, s.length());
return 0;
}
Output :
823
Explanation: all substrings are {8,82,823,2,23,3} and the maximum value substring is 823.
Time complexity: O(n^3)
Auxiliary space: O(n!)
6: Minimum value of all substrings of a string representing a number.
Given an integer represented as a string, we need to get the minimum of all possible substrings of the given string which is representing a number.
Example:
C++
#include <bits/stdc++.h>
using namespace std;
void subString(string s, int n)
{
vector<int> v;
for (int i = 0; i < n; i++){
for (int len = 1; len <= n - i; len++){
string sub =(s.substr(i, len));
int x=stoi(sub);
v.push_back(x);
}
}
cout<<*min_element(v.begin(),v.end())<<endl;
}
int main()
{
string s = "4572";
subString(s, s.length());
return 0;
}
Output:
2
Time complexity: O(N^3)
Auxiliary space: O(N!)
My Personal Notes
arrow_drop_up
