I took a C course some time ago, but I'm only now beginning to use it,
for a personal pet project. My current stumbling-block is finding an
efficient way to find a match between the beginning of a "counted"
string and data in a binary file. Given...
#include <stdio.h>
int main(int argc, char *argv[])
{
char bstring[255];
int bstring_length, match_length;
long match_location;
FILE *input_file, *output_file;
if(argc != 3){
printf(" Correct usage:\n %s input_filename output_filename\n", argv[0]);
return 1;
}
if((input_file = fopen(argv[1], "rb")) == NULL){
printf("Error opening %s for input\n", argv[1]);
return 1;
}
if((output_file = fopen(argv[2], "wb")) == NULL){
printf("Error opening %s for output\n", argv[2]);
return 1;
}
...
Later on, bstring and bstring_length get initialized. bstring may
contain \0's, so the "logical length" (which will not exceed 255) is
actually stored in bstring_length. What I'm trying to do is to find the
location and length of the longest match from the left side of bstring.
If that's not clear, here's an example...
bstring[0] = 'a';
bstring[1] = '\0';
bstring[2] = 'b';
bstring[3] = 'c';
bstring[4] = 'd';
bstring_length = 5;
Assume that the sequence is not matched anywhere in the file. However,
assume that the sequence 'a', '\0', 'b', 'c' does exist in the file.
What's the most efficient search that returns match_length ( 4 ) and
ftell() of the beginning of the match? If it's a function, should I
declare in main() like so?
int bstring_length, *match_length;
long *match_location;
I assume that the function prototype would be something like...
int findmatch( bstring[255], bstring_length, match_length, match_location);
By passing pointers, I assume that both match_location and
match_length will be modified and available to main(). Or is my
understanding of pointers lacking. findmatch() should return 0 if a
match is found, and 1 if no match. Would memory-mapped files help here?
--
Walter Dnes; my email address is *ALMOST* like wz*******@waltdnes.org
Delete the "z" to get my real address. If that gets blocked, follow
the instructions at the end of the 550 message.
