warning: deprecated conversion from string constant to 'char*'

Can someone solve this?.
I have this code which gives me the warning

warning: deprecated conversion from string constant to 'char*'

but if i put const in front of the char* inside struct and update the functions it is perfectly fine.

Can someone tell what's the reason is?

code without const..

Code:

#include <iostream>
using namespace std;
#include <string.h>

enum operator_kind {
    OP_plus, OP_minus,
 
};
struct NameId {
	 char *name;
	int  id;
};
static NameId opname[] = {
	"plus", OP_plus,
	"minus", OP_minus,
	NULL,
};
 char *value2name(NameId *table, int value) ;
 char *op2name(int op);

int main()
{
      char *p;
      p=op2name(1);
      cout<< p  <<endl;
}
char *value2name(NameId *table, int value) 
{
	for (int i=0; table[i].name; i++) {
		if (table[i].id == value)	return table[i].name;
	}
	return 0;
}
char *op2name(int op)
{
	return value2name(opname, op);
}

code with const added

Code:

#include <iostream>
using namespace std;
#include <string.h>

enum operator_kind {
    OP_plus, OP_minus,      
};

struct NameId {
	const char *name;
	int  id;
};

static NameId opname[] = {
	"plus", OP_plus,
	"minus", OP_minus,
	NULL,
};

const char *value2name(NameId *table, int value) ;
const char *op2name(int op);

int main()
{
  
     const char *p;
      p=op2name(1);
      cout<< p  <<endl;
}
const char *value2name(NameId *table, int value) 
{
	for (int i=0; table[i].name; i++) {
		if (table[i].id == value)	return table[i].name;
	}
	return 0;
}

const char *op2name(int op)
{
	return value2name(opname, op);
}

-Thank you

i dont see any need for "#include <string.h>", so try and remove that. if you eventually are going to use C++ strings then #include <string> (no ".h"), if you need to use C-style string functions then #include <cstring>.

does the warning give a line number? what is the command with arguments you use to compile? what compiler are you using?

i dont get that warning in your first code. i am using the mingw gcc that came with DevC++ (gcc 3.4.2 i think). options used were "-pedantic -Wall -Wextra"

Thanks for the reply. But removing string.h didn't help. The warning is on line 17.
End of "};" in the code segment .

Code:

static NameId opname[] = {
	"plus", OP_plus,
	"minus", OP_minus,
	NULL,
};

I am using g++ 4.2.3 in linux (ubuntu)

see the comments in your code. besides those i dont know.

Code:

enum operator_kind {
    OP_plus, OP_minus,    /* trailing comma should be removed */
 
};

static NameId opname[] = {
	"plus", OP_plus,
	"minus", OP_minus,
	NULL,   /* same */
};

Originally Posted by nadroj

see the comments in your code. besides those i dont know.

Code:

enum operator_kind {
    OP_plus, OP_minus,    /* trailing comma should be removed */
 
};

static NameId opname[] = {
	"plus", OP_plus,
	"minus", OP_minus,
	NULL,   /* same */
};

I'm pretty sure it is valid C or C++ to have a trailing comma.

I would suggest that you don't put namespace declarations BEFORE header files:

Code:

using namespace std;
#include <string.h>

That can lead to extremely strange effects and errors that you can't understand.

--
Mats

Your code declares a non-const pointer to a string literal. String literals may be stored directly in the read-only portion of a data segment in your exe. By taking a non-const pointer to one of these you're saying that you might try and modify it, but you're not allowed to modify a constant!
By declaring it as const you're telling the compiler that you just want a pointer to that read-only string literal.

And yes, it's perfectly okay to have a trailing comma in an enum list. In fact it's good form to do this and have each enum on a seperate line, and that way additions look cleaner to a diff program.

Question:
Did a book or a teacher teach you to use char *var?
Do you that alternatives, such as char* var and char * var exist?

I also get the warning that you miss an initializer for NameId::id. Don't know if this affects your code but it is better:

Code:

static NameId opname[] = {
	"plus", OP_plus,
	"minus", OP_minus,
	NULL, 0, 
};