Extract or (even better) change first symbol of char*'s string

Question

1. Is there any way to extract the first (or second, third, whichever) symbol of a string, using only a char* pointer to it?

   char* str = "abcde";
   char* symbol;
   
   // Some actions
   
   std::cout << *symbol; // a in output
   

2. Is there any way to change a certain symbol of a string, using only a char* pointer to it?

   char* str = "abcde";
   
   // Some actions;
   
   std::cout << str; // 1bcde in output
   

   UPD: Note that, according to the task given, I should do it by using char*, not char[] (although if it were not a task, I would definitely use char[]).

Answer 1

The problem you have is that this line

char* str = "abcde";

is wrong, and the compiler even should have complained about that. It should be

   const char[6] str = "abcde";
// ^^^^^

because you can't change anything in the literal.
Or simply do:

   const char[/* length is implicit */] str = "abcde";

anyway you'll end up with a const char[6] array variable.

1. Is there any way to extract the first (or second, third, whichever) symbol of a string, using only a char* pointer to it?

To access a single character you can use just indexing ...

std::cout << str[0] << std::endl; // prints a

2. Is there any way to change a certain symbol of a string, using only a char* pointer to it?

... but you can't change that value by any means.

Answer 2

OK, you are asking questions, and giving example code. As others have mentioned, there is a bit of a mismatch.

In your example code, you write:

char* str = "abcde";

The string literal can't be changed (and it is being assigned to a pointer which is not const; this is an error, as others have mentioned).

Yet you explain that you were given a task which requires changing it!

So, either: 1. Your example to us does not really reflect the task or 2. You are misunderstanding the task or 3. The task is incorrect.

Perhaps the task expects you to work with char *, and you decided on your own to initialize it as you did.

If so....

You need to define a char * which can be modified. For example:

char str1[MAX_CHARS]; // you'll have to define MAX_CHARS as something reasonable
strcpy(str1, "abcde"); // you'll have to make sure that str1 is large enough
char * str = str1;

that is just one example. You can allocate str on the heap if you want, using "new".

Once you have a modifiable string, you can do the things you asked: 1.

char* symbol = &str[0];

std::cout << *symbol; // a in output

or, more directly:

std::cout << str[0]; // a in output -- add an end of line if you need it

2. Modify the string:

   char* str = "abcde";

   str[0] = '1';

   std::cout << str; // 1bcde in output

This is, again, once you have a modifiable string. I am guessing that you really want to know how to properly access a specific point in the string and either use or modify it, and the constness was simply a mistake in your example.

Answer 3

I've just found the answer to my question by myself.

1. I can definitely extract symbols from char* by [] operator.

char* str = "abcde";
std::cout << str[0]; // a
std::cout << str[1]; // b
// and so on

2. I can change the first symbol of the string using char* pointer by following actions:

char* str = "abcde";

char* sym = "1";
str++;
char* rest = str;

str = (char*) malloc((strlen(sym) + strlen(rest)) * sizeof(char));

strcpy(str, sym);
strcat(str, rest);

In my real task I just needed to change the first symbol of a string, so mission completed.