Question

I try to compile with gcc version 4.3.2 20081105 (Red Hat 4.3.2-7) (GCC)
The input file has a const char :

#include <stdio.h>
#include <stdlib.h>
#include "textfile.h"
...
const char * vs=NULL;
vs = textRead("myfile.file");
const char * vv = vs;
free(vs);

This chars vars are used into main cpp program and will be fill with text.

I use in header one function textRead to load the data from myfile.file

I got this error ( I thinking is a cast conversion ) but don’t know where I make mistakes.

warning: deprecated conversion from string constant to ‘char*’
error: invalid conversion from ‘const void*’ to ‘void*’

first warning is about vs = textRead(“myfile.file”);
second error is about free(vs);

What is wrong with my code ?

Answer 1

You haven’t posted what the textRead function looks like, so I’m assuming its signature is as follows:

void *textRead( char *filename );

textRead is taking the name of a file to read, it doesn’t (shouldn’t) need to modify the string passed to it, so change textRead to

void *textRead( char const *filename );

If you cannot modify the function, change your code to

char filename[] = "myfile.file";
vs = textRead( filename );

The error message about free is pretty self-explanatory, free expects a void * and you’re passing it a const pointer instead. I don’t see any reason why vs needs to be a const char * instead of a char *. Change that and the error will go away.

Also, I don’t understand why you’re making a copy of vs right before freeing it, but maybe you haven’t posted stuff that happens in between those 2 lines.