change char* to '*'

[ylxin1993]

I made a class:

class CMessage {
char* pMessage;
public:
void Reset() {
	char* temp = pMessage;
	while(*temp) {
		*(temp++) = '*';
	}
...
};

when I use the Reset method, all my CMessage object's memeber pMessage will be '*', I'm wonder why when I write this, it doesn't work, and output nothing:

void Reset() {
	while(*pMessage) {
		*(pMessage++) = '*';  // why this doesn't work??
}

and I also write these in

main()

just for test:
//test1

char* pMessage = "sharen";
char* temp = pMessage;
*temp = 'u';
cout << pMessage << endl;

//test2

char* pMessage = "sharen";
char* temp = pMessage;
while(*temp) {
	    *(temp++) = '*';
}

I think the test2 maybe work, but none of them work, they output nothing.

and when I write

char* pMessage = "sharen";

, the compiler says

deprecated conversion from string constant to 'char*' [-Wwrite-strings

, what should I do, just ignore it?

[vlad from moscow]

I will start from the last your complaint.:)

String literals in C++ have type const char []. So it will be more correctly to write
const char *pMessage = "sharen";

As for the code

void Reset() {
	while(*pMessage) {
		*(pMessage++) = '*';  // why this doesn't work??
}

I do not see where the memory was allocated that you are trying to fill in. Where does pMessage point?

[ylxin1993]

if I write like this const char *pMessage = "sharen";, what if I want to change the pMessage?

for the code

void Reset() {
	while(*pMessage) {
		*(pMessage++) = '*';  // why this doesn't work??
} 

I don't totally understand what you say upper, could you explain to me more ? why have to make a temporary variable?

and why I write this in the main() function, it outputs nothing:

char* pMessage = "sharen";
char* temp = pMessage;
while(*temp) {
	    *(temp++) = '*';
} 

[BlackSheep]

pMessage points to a string literal, which can't be modified. (Undefined behavious, usually a segfault because you're trying to write to read only memory)

Even if you create the pointer temp, it still points to the same non-modifiable memory.

To create the string as modifiable, make it an array:

char Message[] = "String";
char *pMessage = Message; //Create a pointer to the array 

Even better, use std::string and save yourself a lot of hassle:

std::string Message("String");

[ylxin1993]

pMessage points to a string literal, which can't be modified.
why use a pointer can indirect modify it, like

void Reset() {
	char* temp = pMessage;
	while(*temp) {
		*(temp++) = '*';
	}

[BlackSheep]

Your compiler might not be sticking it into ROM, it's undefined behavior. I guess I should have said "Not supposed to be modified".

If you want to create a pointer to a string literal you should always label it as const.