CString size class

Question

How to increase the size of the CString, if CString Object get maximum size. or tell me the function which can hold maximum data more than the CString

Answer 1

CString uses heap allocation for the string buffer so actual limit for the string length depends on a number of conditions and is some hundreds megabytes.

In general, each time the string needs to grow its buffer it allocates a new buffer greater then the previous one - there's a strategy for how to determine the new size of the buffer. Depending on actual amount of available memory in the system this reallocation may either fail or succeed. If it fails you have very little options of what you can do - the best choice is usually to restart the program.

For the task you solve - working with a COM port - you can use an MFC::CArray which is very convenient to use as a variable size array. You could also use std::vector for the same.

Answer 2

In CString, the string actual size and allocated buffer are held by signed ints (check out CStringData). The string buffer itself is dynamically allocated. This means the theoretical limit is 2^31 characters. Practically, on a 32 bit environment you'll be able to get much less due to memory fragmantation. Also, if you're using Unicode CString, each character is two bytes, which means the CString buffer will hold less text. On a 64 bit environment you might be able to get as much as 2^31 characters.

Having that said, are you really trying to work with strings that long? There's probably a lot to do before you hit the CString length limit.