Thread: Using variables as place markers for strings?

(Sorry if the title does not really match the question.)

I have been hardcoding filenames into my code but have been told that that is error prone and hard to maintain.
I have tried to recode to achieve this but am getting complier errors.
As an example I have a file name declared and defined as shown below.

Code:

char index_file[10] = "index.dat"; //correctly formatted files stored in here

Further on in my code I have need to use that file name. At present I need to hard code it in e.g.

Code:

strncat(shorttiffUrl, "index.dat", 40);

Is it possible to replace the index.dat by something that points to the original declaration?
I have tried

Code:

strncat(shorttiffUrl, index_file, 40);

and

Code:

strncat(shorttiffUrl, *index_file, 40);

but both give complier errors e.g

Code:

C:/ScanImages/findRPTfiles-4.cpp: In function `int main(int, char**)':
C:/ScanImages/findRPTfiles-4.cpp:204: error: invalid conversion from `char' to `const char*'
C:/ScanImages/findRPTfiles-4.cpp:204: error:   initializing argument 2 of `char* strncat(char*, const char*, size_t)'
mingw32-make.exe[1]: *** [Debug/findRPTfiles-4.o] Error 1

I am sure that the answer is staring me in the face but I cannot see it.
I know that this will be useful for later in my nascent coding career.

Should work fine. Can you post a small, compilable program that can reproduce the error?

More specifically, the first one should work fine and the second one should die a horrible death.

Also, both strncpy and strncat are broken, IMO. The first isn't guaranteed to append a null terminator, and the latter adds the length of the destination string to the length parameter to obtain the maximum total size of the string. Both of these could lead to some nasty bugs. Here are a couple of 'safe' replacements:

Code:

char* sstrncpy( char* dst, char const* src, size_t max )
{
	char* 
		ptr = dst;
	if( max != 0 )
	{
		while( --max && *src )
			*ptr++ = *src++;
		*ptr = 0;	
	}
	return dst;
}

char* sstrncat( char* dst, char const* app, size_t max )
{
	char* 
		ptr = dst;
	if( max != 0 )
	{
		while( --max && *ptr )
			++ptr;
		while( max-- && *app )
			*ptr++ = *app++;
		*ptr = 0;	
	}
	return dst;
}

Et al
I found an error earlier in the code. Having a lower case letter rather than an upper case can pose problems.

Thank you for your replies.

Originally Posted by Sebastiani

Also, both strncpy and strncat are broken, IMO. The first isn't guaranteed to append a null terminator, and the latter adds the length of the destination string to the length parameter to obtain the maximum total size of the string. Both of these could lead to some nasty bugs. Here are a couple of 'safe' replacements:

Code:

char* sstrncpy( char* dst, char const* src, size_t max )
{
	char* 
		ptr = dst;
	if( max != 0 )
	{
		while( --max && *src )
			*ptr++ = *src++;
		*ptr = 0;	
	}
	return dst;
}

char* sstrncat( char* dst, char const* app, size_t max )
{
	char* 
		ptr = dst;
	if( max != 0 )
	{
		while( --max && *ptr )
			++ptr;
		while( max-- && *app )
			*ptr++ = *app++;
		*ptr = 0;	
	}
	return dst;
}

Sebastiani
In an earlier thread you showed me the sstrncpy and I have used it in my code. it works well. I will try the sstrncat.