How to change a variable from const char* to c8*?

[Morgawr]

Hello everyone, I have a little minor problem...

I have gotten from an XML file an attribute as a const char* using the XMLFile->getAttributeValue("attribute_name") and I want to save it into a c8* variable (because that's what I use in my program). How can I convert it? I tried casting it but the "const" attribute to the variable bothers me a little.. I think I lack some C++ basic knowledge for this maybe? I don't know can someone very please help me?

[Bersi]

Do you want to copy the string/data or do you only want to save the pointer?

In first case you can use some C-functions like strncpy or sprintf:

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const char* source = "Hello World";
c8* dest = new c8[100];
strncpy(dest, source, strlen(source)); // way 1
sprintf(dest, "%s", source); // way 2

In second case you can use const c8* instead of c8*. Or you have to use const_cast. In most cases const_cast is an indication for bad code design. This means in most cases you don't need to cast a const char* to a char* because then you can change the pointer, while the const don't allow it.


Btw, c8 and char are equal data types.

[Morgawr]

Do you want to copy the string/data or do you only want to save the pointer?

In first case you can use some C-functions like strncpy or sprintf:

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const char* source = "Hello World";
c8* dest = new c8[100];
strncpy(dest, source, strlen(source)); // way 1
sprintf(dest, "%s", source); // way 2

In second case you can use const c8* instead of c8*. Or you have to use const_cast. In most cases const_cast is an indication for bad code design. This means in most cases you don't need to cast a const char* to a char* because then you can change the pointer, while the const don't allow it.

No no I just need to copy the text so I guess I could use that code... Do I have to import some C headers in order to use that?

[hybrid]

Better use the string classes core::Stringc and core::Stringw for these purposes. Otherwise you have to cope with all the memory allocation stuff like in plain C.

[Morgawr]

Better use the string classes core::Stringc and core::Stringw for these purposes. Otherwise you have to cope with all the memory allocation stuff like in plain C.

ehm? Where do I find those? They are in Irrlicht?

can you post an example code please?

[rogerborg]

They're in include/irrString.h. Just include irrlicht.h

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const char * text = "Some text";
irr::core::stringc copyOfText(text); // or just do using irr; using core;
(void)printf("%s\n", copyOfText.c_str());

Of course, stringc::c_str() returns const char *, so I guess you're still boned if you want to avoid casting.

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#include <string.h>
const char * text = "Some text";
c8 * copyOfText = strdup(text);

// But at some point you must remember to do this:
free(copyOfText);

[Bersi]

Google is your friend!

sprintf: #include <stdio.h> or better #include<cstdio>
strncpy: #include <string.h> or better #include <cstring>

For C++ strings: #include <string>


Then you can use it:

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const char* Source = "Hello World";
std::string MyString = Source;

If you don't want to add the std:: you have to add the following line one time:

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using namespace std;

[Acki]

I would use the string class from Irrlicht (I love it), like rogerborg said...
for the future you should also have a look for the array class from Irrlicht, it's prety usefull, too !!!

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#include <string.h>
const char * text = "Some text";
c8 * copyOfText = strdup(text);

// But at some point you must remember to do this:
free(copyOfText);

I don't think this is necessary, because c8 is nothing more than char...
OK, if a function wants a c8* and the compiler throws an error about passing a char* you'll have to do a type cast, but in my oppinion this is better than this strdup...

also with the string class you can create strings of either type:

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string<char> cString;
string<wchar_t> wString;
string<c8> c8String;

[rogerborg]

I don't think this is necessary, because c8 is nothing more than char...

I'm assuming that Morgawr intends to modify the contents of the memory (or else he'd be using const c8 *), and so he has to duplicate the memory returned from XMLFile (which is declared to be const).

[hybrid]

I guess it's best to store and manipulate inside the stringc class... So what are you actually doing with the c8*?

[Morgawr]

I must apologize for my newbiness here now..
I took a whole day of lurking in the API and I honestly didn't notice stringc and stringw before in Irrlicht..

I was basically using c8* as a string but since now I've found stringc and stringw, I'm sticking to them! Sorry for this stupid thread, I should have lurked a bit more before asking these kind of questions but I was a bit desperate because my program wasn't running (now it does)

so thank you all for your quick and very interesting answers

[Acki]

I should have lurked a bit more before asking these kind of questions

this is always a good idea !!!