Question

I have a working code using OPENFILENAME. May i know how to use strcat to dynamically control the its parameters

this one is working

//ofn.lpstrFilter = "Rule Files (*.net and *.rul)\0*.rul;*.net\0";   

char filter[100];  
char filterText[100];  
char filterVal[100];
strcpy(filterText, "Rule Files (*.net and *.rul)");   
strcpy(filterVal, "*.rul;*.net");   

I tried using strcat first with ‘\0’ but it only only shows like this
strcat (filter, filterText);
strcat (filter,"\0");
strcat (filter,filterVal);
strcat (filter,"\0");
ofn.lpstrFilter = filter; \\missing \0

And I tried using ‘\\0’
strcat (filter, filterText);
strcat (filter,"\\0");
strcat (filter,filterVal);
strcat (filter,"\\0");

ofn.lpstrFilter = filter; \\now includes the\0

but when i run the program the dialogue box filter shows like this
“Rule Files (*.net and *.rul)\0*.rul;*.net\0”;

thanks

Answer 1

Using "\\0" won’t do anything useful, that will just put the literal two characters \0 in your string when you want a nul byte. However, strings in C are terminated by '\0' so you can’t use strcat to construct a nul delimited string without a bit of pointer arithmetic.

So, given these:

char filterText[] = "Rule Files (*.net and *.rul)";
char filterVal[]  = "*.rul;*.net";
char filter[100];

You’ll need to do something like this:

/*
 * The first one is a straight copy.
 */
strcpy(filter, filterText);

/*
 * Here we need to offset into filter to right after the
 * nul byte from the first copy.
 */
strcpy(&filter[strlen(filterText) + 1], filterVal);

A better approach would be to allocate your filter with malloc so that you don’t have to worry about buffer overflows:

char *filter = malloc(strlen(filterText) + 1 + strlen(filterVal) + 1);