I tried printing the string I created, but it doesn't exist. As you can see, the output shows length is 0:
#include <iostream>
#include <string>
using namespace std;
int main(){
string a="";
a[0]='a';
a[1]='b';
a[2]='c';
cout<<"length of a: "<< a.length();
}
Output to the console is:
length of a: 0
You code has undefined behavior because you access elements out of bounds. The string has size() (which is the same as length()) 0 so a[0] and the others access elements that don't exist.
To make it work, you must resize() the string first.
Example:
string a;
a.resize(3);
a[0]='a';
a[1]='b';
a[2]='c';
You can also create the string with the proper length directly:
string a(3, '\0'); // create a string of length 3 filled with \0 chars
You are trying to acces an element whhich hasn't existed yet.
a is an empty string so has size of 0, hence a[0] is undefined behavior because the size at least should be 1.
To avoid that use resize() before assigning to a, as follows
#include<iostream>
#include<string>
using namespace std;
int main(){
string a="";
a.resize(3);
a[0]='a';
a[1]='b';
a[2]='c';
cout<<"length of a: "<< a.length();
}
Or use push_back, as follows
#include<iostream>
#include<string>
using namespace std;
int main(){
string a="";
a.push_back('a');
a.push_back('b');
a.push_back('c');
cout<<"length of a: "<< a.length();
}
The first solution is better than the second to avoid reallocating.
Also see this Why is "using namespace std;" considered bad practice?
1)This string a=""; length of character here is 0 so it size also 0.
2)
a[0]='a';
a[1]='b';
a[2]='c';
it undefined behavior You are accessing out of bounds
3)so Add a.resize(3); to your code that is
#include<iostream>
#include<string>
using namespace std;
int main()
{
string a="";
a.resize(3); // this will resize
a[0]='a';
a[1]='b';
a[2]='c';
cout<<"length of a: "<< a.length();
}
Or string a="xxx"; fill some characters initially or use push_back(); like
a.push_back('a');
a.push_back('b');
a.push_back('c');
You should probably build a char array, and then you can use the from sequence string constructor.
