this little program describes my problem which I have in bigger project:
int main()
{
string str1="11111111";
string str2="22222222";
char a=str1[2];
char *a1=&a;
int var1= atoi(a1);
char b=str2[2];
char *b1=&b;
int var2= atoi(b1);
cout<<var1<<endl;
cout<<var2;
return 0;
}
Why I'm getting
1
21
istead of
1
2
?
Is there any way to fix this? - thanks for the help I trying to figureout for two hours
You get both results by mistake (even though your first result happens to match your expectation).
The problem is that both a1 and b1 point to a single character, while atoi expects a null-terminated string.
You can fix this problem by constructing character arrays instead of copying individual characters:
char a1[2] = { str1[2] }; // C++ compiler supplies null terminator, you supply the size
int var1= atoi(a1);
char b1[] = { str2[2], 0 }; // You supply null terminator, C++ compiler computes the size
int var1= atoi(b1);
Use std::stoi() and std::string::substr() especially if you have std::string already:
std::string str1="11111111";
std::string str2="22222222";
int var1= std::stoi( str1.substr( 2, 1 ) ); // third symbol, 1 symbol long
int var2= std::stoi( str2.substr( 2, 1 ) );
atoi expects a pointer to a null-terminated string of char. You pass a pointer to a char. What happens is undefined. You better use std::stoi instead of atoi since atoi has some fallacies: What is the difference between std::atoi() and std::stoi?
atoi wants a pointer to the first element of a zero-terminated sequence of characters.
You're passing it a pointer to a single character, leaving undefined behaviour in your wake.
To get the integer value of one of the digits, take its distance from '0':
int var = str1[2] - '0';
'0'(character literal, not integer literal), assuming a character set where all numbers are listed sequentially.