Is C-style string unchangable?

[Xiaoshen Li]

Dear All,

I hear a lot that cstring cannot be changed. But my code:

/************************************************** ***********
* Testing cstring(a pointer)
* ************************************************** ********/
#include <iostream>
using namespace std;

int main()
{
char shortsTring[] = "abc";
shortsTring[2] = 'X';

cout << shortsTring << endl; //print out abX !!!

return 0;
}

So why many people are saying cstring cannot be changed? Could you help
me? Thank you very much.

[Mike Wahler]

"Xiaoshen Li" <xl**@gmu.edu> wrote in message
news:dp**********@osf1.gmu.edu...

Dear All,

I hear a lot that cstring cannot be changed.

If by 'cstring' you mean the 'C-style string', i.e. a zero-terminated
array of characters, then you heard wrong. For various reasons, *some*
C-style strings are not modifiable in a defined way. To state this about
*any* such string is simply wrong.

What cannot be modified is an array whose elements are const:

const char arr[] = "Attempts to modify this string"
" should result in compiler diagnostic";

or a string literal:

char *p = "I am a literal";

p[0] = 'i'; // undefined behavior.
But my code:

/************************************************** ***********
* Testing cstring(a pointer)
There are no pointers declared or defined in your code.
* ************************************************** ********/
#include <iostream>
using namespace std;

int main()
{
char shortsTring[] = "abc";
This is an array of four type 'char' objects. It is not a pointer.
shortsTring[2] = 'X';
This replaces the object at shortsTring[2] with the character value 'X'
The string now contains: "abX"

cout << shortsTring << endl; //print out abX !!!
This is expected and normal behavior. You created a 'normal'
non-const (i.e. modifiable) array of characters, changed the
value of one of those characters, then inserted all the characters
into the output stream designated by 'cout'.

Which C++ book(s) are you reading?

return 0;
} -
So why many people are saying cstring cannot be changed?
Two possibilites:
1. They're simply wrong.
2. You've misunderstood.

Depending upon context, some objects are modifiable, others are not.
The types of these objects (such as char, or arrays thereof), makes
no difference.
Could you help me? Thank you very much.

The best help I can offer is to advise you to abandon the use
of character arrays for representing strings in C++, and use
the 'std::string' type (declared by <string>), which was created
specifically for the purpose.

-Mike

[Jim Langston]

"Xiaoshen Li" <xl**@gmu.edu> wrote in message
news:dp**********@osf1.gmu.edu...

Dear All,

I hear a lot that cstring cannot be changed. But my code:

/************************************************** ***********
* Testing cstring(a pointer)
* ************************************************** ********/
#include <iostream>
using namespace std;

int main()
{
char shortsTring[] = "abc";
shortsTring[2] = 'X';

cout << shortsTring << endl; //print out abX !!!

return 0;
}

So why many people are saying cstring cannot be changed? Could you help
me? Thank you very much.

constant "cstring" (c style strings) can not (should not) be changed. It is
fine to change non constant c style arrays as you've seen.

Whoever told you that all c style strings can not be changed was simply
wrong. A C style string is simply an array of characters which is null (0)
terminated. Nothing more, nothing less. You can change the data just as
you can change any array data.

Note the difference between:
char* shortsTring = "abc"; // shortsTring points to constant data
and
char shortsTring[] = "abc"; // shortsTring is an array of non constant data