Thread: c and c++ string

It's actually "string" or "std::string" and long answer short - it's a class.
Internally, it uses a C-style string but with dynamic memory management.

Originally Posted by sick

my question is how c++ allocates some space in storing characters in data type string?
cause in c we all knew we should declare how many characters will be allocate and the
problem with c strings is the SIZE for example if the SIZE is equal to 5 then we input
more than 5 characters then we are sure that there would happen unusual unlike in
c++...

I actually don't know C++ so I don't know the syntax for that, but I do know that most languages (other than C) have a "string" datatype. C does not have a "string" datatype, a "C string" is a char array. Also, C arrays are not dynamic, so their SIZE must be defined at compile time.

This is an aspect of the "low-levelness" of C, since you could implement a dynamic array or String datatype using low-level procedures:

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef char* String;

String newString (char *content) {
	String new=malloc(strlen(content)+1);
	strcpy(new,content);
	return new;
}

int main() {
	String eg=newString("hello world");
	printf("%s\n",eg);
	free(eg);
	return 0;
}

Notice you can use this String datatype uncast with string functions since it is just a char pointer. However, it is committed to being a heap variable and so must be free()'d, and does not resize itself dynamically (you could write functions for that too, but probably the normal string functions will do).

Other languages which do have such a datatype use routines like this internally to support them. For example, in C++ a String is an object. If you wade through the source for your C++ library or something you should be able to find the exact code which creates Strings and it probably has a char* somewhere in it...as Elysia implies.

It's better to say that "string" is a class, because an object is an instantiated class. And it's not "String," it's "string" since C++ is also case sensitive.
And yeah, std::string pretty much works like that. It also keeps track of size.

The std::string class is of the same class as std::basic_string. Also using char *string is more common than using a character array in C.

Originally Posted by P4R4N01D

Also using char *string is more common than using a character array in C.

*string is a pointer to a character array.

Originally Posted by P4R4N01D

The string class is an instance of basic_string, which is a class.

No it isn't. std::string is a typedef for std::basic_string<char, char_traits<char>, allocator<char> > not an instance.

Cprogramming.com FAQ > Dynamic Memory Allocation: new and delete (C++)

Originally Posted by sick

umm btw what is the new keyword??

Are you learning C or C++? If you are learning C, then do not worry about it since it will not concern you. If you are learning C++, then ask your question in the C++ forum (but you should be reading a tutorial instead of asking such a question). If you are trying to learn both simultaneously, then you are better off picking one to learn first.

Originally Posted by Elysia

It's actually "string" or "std::string" and long answer short - it's a class.
Internally, it uses a C-style string but with dynamic memory management.

That's poor of you to make assumptions about its implementation

Originally Posted by zacs7

That's poor of you to make assumptions about its implementation

I suppose, but I don't see many implementations doing it differently.