Passing string literal to function taking 'char *' and getting a compiler warning

Question

Just a syntax question, here is my code snippet. (Sorry, browser isn't letting me paste properly into stack overflow.)

#include <iostream>     /* 'iostream.h' is deprecated. */
#include <cstring>
#include <cstdlib>
#include <cstdio>

using namespace std;    /* Required. */

FILE *OpenFile(char *Filename)
{
        FILE *FP;

        if((FP = fopen(Filename, "r")) == NULL)
        {       /* Error opening file. */
                std::cout << "[!!] Unable to open database!"
                          << " Are you sure it exists?\n"
                          << "[<<] Database Unchanged.\n";
                exit(EXIT_FAILURE);     /* End program. */
        }

        else    /* Properly opened the file. */
                return FP;
}

int main(void)
{
        FILE *Data;     /* Our database file pointer. */
        Data = OpenFile("Data.txt");
        printf("Success!\n");
        return 0;
}

When I compile, I get the following warning:

$ g++ test.cpp -o test
test.cpp: In function ‘int main()’:
test.cpp:27:28: warning: deprecated conversion from string constant to ‘char*’ [-Wwrite-strings]
$

Where am I going wrong?

Please paste your code here. Don't make us visit an external site to see your code. — Carl Norum
– Carl Norum, Commented Mar 3, 2012 at 4:22
I know, firefox has been acting weird for me, trying to figure out why. — Irresponsible Newb
– Irresponsible Newb, Commented Mar 3, 2012 at 4:24
Report errors on cerr; that's what it is designed for. And, in theory, it would be a good idea to use FILE *Data = OpenFile("data.txt"); and to close the file before exiting. In practice, in this context, it does not matter much, but in many contexts, not freeing allocated resources is a bad idea, and RAII (Resource Acquisition Is Initialization) suggests the initialize on definition notation. — Jonathan Leffler
– Jonathan Leffler, Commented Mar 3, 2012 at 4:32

rob mayoff · Accepted Answer · 2012-03-03 04:25:54Z

12

String literals in C++ are of type “array of n const char” (where n is the number of characters in the string, including the terminating NUL). Declare your function this way:

FILE *OpenFile(const char *Filename)

answered Mar 3, 2012 at 4:25

rob mayoff

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