I have a char array which is VERY large and I iterate through the array. I look for patterns with logic such as:
if (array[n] == 'x' and array[n+1] == 'y' and array[n+2] == 'z')
{
mystring = array[n+4] + array[n+5];
}
if array[n+4] is '4' and array[n+5] is '5' then mystring = "45"
However, mystring is always "", what am I doing wrong? I don't want to use substring as the array is too large. I just want to cast the chars to strings and then append to mystring.
I suggest so use assign(const char*, len); no copy constructor is involved
if (array[n] == 'x' and array[n+1] == 'y' and array[n+2] == 'z')
{
mystring.assign(array + n + 4, 2);
}
You're checking for a consecutive "xyz" occurrence , why not simply use std::string ?
std::string s(array);
size_t i =s.find("xyz");
if(i!=std::string::npos && i+5 <= s.size())
{
std::string mystring = std::string(1,array[i + 4]) + array[i + 5];
std::cout<<mystring;
}
You can cast chars to ints and vice versa because they are basic language types. Strings are implemented as a class so you need to invoke the string constructor for both chars then concatenation the two resulting strings into mystring
If you can't use std::string in the first place, as suggested by @P0W (which is a good suggestion), then there is another alternative to do this conversion that does not involve string constructor (I think the solution using string constructor is a great one, but knowing different approaches can give you more flexibility), but relies on std::string::append.
int main ()
{
// create char
char *str1 = new char[6];
strcpy( str1,"hello ");
char *str2 = new char[5];
strcpy(str2, "world" );
// use of append to convert to a string
std::string mystring;
mystring.append(str1);
mystring.append(str2);
std::cout << mystring << std::endl;
}
Check the std::string::append documentation, and you will also see that one of the overloading of this functions is string& append (const char* s, size_t n), which means you can convert just subset of char arrays, as you request it.
Adding characters strings doesn't work like that in C++. The easier way to do this is to create a stringstream and add the characters to the string with the << operator, then recover a string from it using the str() method.
Example:
#include <iostream>
#include <sstream>
using namespace std;
int main(void)
{
char a[] = {'a', 'd', 'c', 'b', 'a' };
stringstream linestream;
linestream << a[0] << a[1];
cout << linestream.str() << endl; // Prints ad
return 0;
}
myString = std::string(array[n + 4]) + array[n + 5]for an even shorter variant.std::string mystring = std::string(1,array[i + 4]) + array[i + 5];as none of the constructor takes justchararray[n+4] + array[n+5]doesn't do what you think it does. It takes the two characters as ASCII values and adds them together to create a new single character. It doesn't create a new string with the two characters concatenated.