Thread: Improving the efficiency..

Hey all, recently I've played around with pointers and some win32 API and I've came up with this portion of code, to basically load a set of string from a file on a secondary storage, store it in the memory and then print it on the screen. The apparent problem is that this code draws slowly comparatively with printf function. I don't want to use printf because i am limited to the coordinates (0,0) only. I want to be able to print anywhere on the screen preserving the format of my string. So basically this function is able to do it but doing it slowly. This happen only if the string happens to be large, like maybe 4kb? So I am wondering is there anyway that i can optimize it? I am suspecting that the problem comes from the while loop that I used to individually scan the string for any escape character inorder to process new line therefore to preserve the user-defined coordinates. (My function printSTR allows the user to print the string on a specific location of a screen instead of printf which only prints from (0,0). )

Code:

//////////////////////////////////////////////////////////////////////////////
// void printSTR(char *text, int x, int y)
// Author:   -aaronljx-
// 
// To print a string to the console screen from a file preferably, you need
// to call the function LoadSTR first before printing it.
//
// Usage:
// char *text    -> pointer to the address of the string
// int x, int y  -> coordinates of where the string to be printed
//
// eg.
// printSTR("This is to print directly", 2, 5);
//
// char *pStr1;
// pStr1 = LoadSTR("file1.txt");
// printSTR( pStr1, 2, 5 );
// free(pStr1);
//
// Note: Make sure you free every string loaded from file with
// the free function, free(var_name);
//////////////////////////////////////////////////////////////////////////////
void printSTR(char *text, int x, int y)
{
	gotoXY(x, y);

	while ( *text )
	{
		if ( *text == 10 ) // if *text returns \n
		{
			y++;
			gotoXY(x, y);
			text++;
		}
		else
		{
			printf("%c", *text);
			text++;
		}
	}

	return;
}

//////////////////////////////////////////////////////////////////////////////
// char *LoadSTR(char *filename)
// Author:   -aaronljx-
//
// This function works hand in hand with the function printSTR
// to load string directly from file and print it on the screen
// on the given coordinates.
//
// Usage:
// char *filename  -> the location of the string in your secondary storage
//
// Returns:
//   -> the address of the loaded string
// eg.
// char *pStr1;
// pStr1 = LoadSTR("file name.txt");
// printSTR( pStr1, 2, 5 );
// free(pStr1);
//
// Note: Each time you load a string from file, make sure you free it
// after using it. This is important.
//////////////////////////////////////////////////////////////////////////////
char *LoadSTR(char *filename)
{
	FILE *buffer;
	char *pString, temp;
	int nChar = 0;

	if ( !( buffer = fopen( filename, "r" ) ) )
	{
		printf("\aError! Unable to open required files.\n");
		getchar();
		exit(EXIT_FAILURE);
	}

	while ( fscanf( buffer, "%c", &temp ) != EOF )
		nChar++;

	pString = (char*) calloc( nChar + 1, sizeof(char) );

	rewind(buffer);
	fscanf( buffer, "%[^\0]", pString );
	fclose(buffer);

	return pString;
}

Originally Posted by matsp

Small improvement would be to use putc() or putchar() instead of printf() - since you are printing a char at a time, it seems unnecessary to use printf which is quite complex.
A bigger improvement would be to printf() large chunks of the string (using something like strchr() to find the newlines).

You can certainly do the same thing in the read, using fgetc() instead of the more complex scanf() function. Reading the same string twice (first scanning, then reading the whole string) seems unnecessarily complicated. Use a scheme where you pre-allocate a small buffer, and grow it using realloc instead. [Or, if you insist on counting the letters first, use fread to read the entire string at once].

Code:

		if ( *text == 10 ) // if *text returns \n
		{
			y++;
			gotoXY(x, y);
			text++;

would it not be clearer to use '\n' instead of 10 - not to mention that it would be portable to a system where 10 is not the quivalent of '\n'. [No, I don't know of any such system - but I wouldn't be surprised if they exist].

Second, isn't x supposed to change to 0 as well for a newline?

--
Mats

Ahh thanks for the advice.. I also thought about writing my own code to format the string, I am thinking that probably after loading the big chunk of string into the memory, I'll create another buffer, calculate the whitespaces required if the user wants to print every line at the coordinate, (5,2) then insert the whitespace into the string and print the whole string as a block. Actually I thought if I use '\n', the compiler automatically changes it to the ASCII counterpart (which is 10) right?

Btw if I use realloc instead, how do I grow it? I don't really know about that function actually. Besides I have also considere using WriteConsoleOutput function as an alternative solution by first creating another screen buffer, draw the whole block on it, then read in the contents to a CHAR_INFO array, then rewrite it on the standard output handle, finally destroy the temporary screen buffer. Any alternatives? Thanks.

Originally Posted by iMalc

This is a very poor and slow way of determining the length of a file:

Code:

	while ( fscanf( buffer, "%c", &temp ) != EOF )
		nChar++;

Then any alternative?

You could try reading up on io.h

http://www.digitalmars.com/rtl/io.html#_filelength

See _filelength function

True matsp. Though their are functions out there for this sort of thing. Listed below as well when googling around.

http://www.warpspeed.com.au/cgi-bin/...PG4REF.INF+121

States this is in the c Library reference.

[Off topic]

Oh I have had no dealings or used code by them, but what is the deal with Digital Mars?

[/Off topic]