Help with this. My error seems to be in trying to get the ? wildcard to function
ID: 3603724 • Letter: H
Question
Help with this. My error seems to be in trying to get the ? wildcard to function properly for the makefile. The ? wildcard works as intended, provided it is not the last character in the search. The line in bold is where the error pops up, I was wondering what part of this is actually causing this error to occur.
rgrep.c
#include <stdio.h>
#define MAXSIZE 4096
char next_char(char *string) {
return *(string + sizeof(char));
}
char prev_char(char *string) {
return *(string - sizeof(char));
}
//Accepts char, not pointer
int is_operator(char pattern) {
switch(pattern) {
case '.' :
return 1;
case '\' :
return 2;
case '+' :
return 3;
case '?' :
return 4;
default :
return 0;
}
}
int plus_modified(char *pattern) {
if(next_char(pattern) == '+')
return 1;
return 0;
}
int question_modified(char *pattern) {
if(next_char(pattern) == '?')
return 1;
return 0;
}
int escape_modified(char *pattern) {
if(prev_char(pattern) == '\')
return 1;
return 0;
}
/**
* You can use this recommended helper function
* Returns true if partial_line matches pattern, starting from
* the first char of partial_line.
*/
int matches_leading(char *line, char *pattern) {
//Check direct match
if(*line == *pattern && !is_operator(*pattern)) {
return 1;
}
//Check wildcard match
if(*pattern == '.' && !escape_modified(pattern)) {
return 1;
}
//Check escaped operator match
if(*line == *pattern && is_operator(*pattern) && escape_modified(pattern)) {
return 1;
}
//Check escape character
if(*pattern == '\')
return matches_leading(line, pattern + sizeof(char));
//Check for absent case of ? operator
if(question_modified(pattern))
return 1;
return 0;
}
/**
* You may assume that all strings are properly null terminated
* and will not overrun the buffer set by MAXSIZE
*
* Implementation of the rgrep matcher function
*/
int rgrep_matches(char *line, char *pattern) {
static int pattern_depth = 0;
//Base cases
if(*pattern == '') {
//Reset pattern for new line
if(*line == ' ') {
pattern -= pattern_depth * sizeof(char);
}
pattern_depth = 0;
return 1;
}
if(*line == '')
return 0;
//Reset pattern for new line
if(*line == ' ') {
pattern -= pattern_depth * sizeof(char);
pattern_depth -= pattern_depth;
return 0;
}
//Check for escape
if((*pattern == '\') && is_operator(next_char(pattern))) {
pattern += sizeof(char);
pattern_depth++;
}
//Check for match
if(matches_leading(line, pattern)) {
//For + modifier
if(plus_modified(pattern)) {
int chars_before = 1;
if(*pattern == *(pattern + 2 * sizeof(char)))
chars_before = 2;
//Go to next nonmatching character
//Stops one before because there is a line increment at the end of rgrep_matches
while(*(line + chars_before * sizeof(char)) == *pattern && !(*pattern == '.' && !escape_modified(pattern)))
line += sizeof(char);
//Handle .+
if(*pattern == '.' && escape_modified(pattern)) {
char wildcard = *line;
while(*(line + chars_before * sizeof(char)) == wildcard)
line += sizeof(char);
}
if(*pattern == '.' && !escape_modified(pattern)) {
//while(*(line + chars_before * sizeof(char)) != *(pattern + 2 * sizeof(char)))
while(!matches_leading(line + chars_before * sizeof(char), pattern + 2 * sizeof(char))){
line += sizeof(char);
if((*line == '' || *line == ' ') && *(pattern + 2 * sizeof(char)) != '')
return 0;
}
}
//Compensate for the character that the operator took
pattern += sizeof(char);
pattern_depth++;
}
//For ? modifier
if(question_modified(pattern)) {
//
if (*pattern == '.' && !escape_modified(pattern) && escape_modified(pattern + 3 * sizeof(char)) && *line == *(pattern + 3 * sizeof(char)) && *(line + sizeof(char)) != *(pattern + 3 * sizeof(char))) {
pattern_depth += 4;
return rgrep_matches(line + sizeof(char), pattern + 4 * sizeof(char));
}
//
else if(*pattern == '.' && !escape_modified(pattern) && *line == *(pattern + 2 * sizeof(char))) {
pattern_depth += 2;
return rgrep_matches(line, pattern + 2 * sizeof(char));
}
//
else if(*pattern == '.' && !escape_modified(pattern) && *line != *(pattern + 2 * sizeof(char))) {
pattern_depth += 2;
return rgrep_matches(line + sizeof(char), pattern + 2 * sizeof(char));
}
//
else if(*line == *pattern && *line == *(pattern + 2 * sizeof(char))) {
pattern_depth += 2;
return rgrep_matches(line, pattern + 2 * sizeof(char));
}
//
else if(*line == *pattern && next_char(line) == *(pattern + 2 * sizeof(char))){}
//
else if(*line == *pattern && next_char(line) != *(pattern + 2 * sizeof(char)) && *line != *(pattern + 2 * sizeof(char)))
{}//return 0;
//
else if(*line != *pattern && *line != *(pattern + 2 * sizeof(char)))
return 0;
//
else if(*line == *pattern && *pattern == '.' && escape_modified(pattern)){}
//
else if(!(*pattern == '.' && !escape_modified(pattern)) || *line != *pattern)
line -= sizeof(char);
//Compensate for the character that the operator took
pattern += sizeof(char);
pattern_depth++;
}
pattern += sizeof(char);
pattern_depth++;
}
//Reset the pattern on partial match so that we only get contiguous matches
else if(pattern_depth != 0 && *(pattern - pattern_depth * sizeof(char)) != '') {
pattern -= pattern_depth * sizeof(char);
pattern_depth -= pattern_depth;
}
//if(*line != ' ')
line += sizeof(char);
//Recurse
return rgrep_matches(line, pattern);
}
int main(int argc, char **argv) {
if (argc != 2) {
fprintf(stderr, "Usage: %s <PATTERN> ", argv[0]);
return 2;
}
/* we're not going to worry about long lines */
char buf[MAXSIZE];
while (!feof(stdin) && !ferror(stdin)) {
if (!fgets(buf, sizeof(buf), stdin)) {
break;
}
if (rgrep_matches(buf, argv[1])) {
fputs(buf, stdout);
fflush(stdout);
}
}
if (ferror(stdin)) {
perror(argv[0]);
return 1;
}
return 0;
}
MAKEFILE for the code
# Your program must compile with 'make'
# You must not change this file.
CC = gcc
FLAGS = -std=c99 -O0 -Wall -Werror -g -pedantic
rgrep:
$(CC) $(FLAGS) rgrep.c -o rgrep
clean:
rm -rf rgrep *.dSYM
check: clean rgrep
test "`echo "a b c" | ./rgrep 'a'`" = "a"
test "`echo "a " | ./rgrep 'a'`" = "a"
test "`echo "a" | ./rgrep '...'`" = ""
test "`echo "abc" | ./rgrep '.b.'`" = "abc"
test "`echo "h aaaaah" | ./rgrep 'a+h'`" = "aaaaah"
test "`echo "h aaaaahhhhh" | ./rgrep 'aa+hh+'`" = "aaaaahhhhh"
test "`echo "h aaaaahhhhh " | ./rgrep 'aa+hh+'`" = "aaaaahhhhh"
test "`echo "a" | ./rgrep 'a?a'`" = "a"
test "`echo "woot wot wat " | ./rgrep 'wo?t'`" = "wot"
test "`echo "CCCCCCC C+ C++" | ./rgrep '.++'`" = "C++"
test "`echo "GG" | ./rgrep '.+'`" = "GG"
test "`echo "woooooo_CSE31.jpg" | ./rgrep 'w.+_...31.jpg'`" = "woooooo_CSE31.jpg"
test "`echo "aab" | ./rgrep 'bb?'`" = "aab"
test "`echo "aaab" | ./rgrep 'a+b'`" = "aaab"
test "`echo "aaab" | ./rgrep 'a+ab'`" = "aaab"
@echo "Passed sanity check."
Explanation / Answer
#include <stdio.h>
#define MAXSIZE 4096
char next_char(char *string) {
return *(string + sizeof(char));
}
char prev_char(char *string) {
return *(string - sizeof(char));
}
//Accepts char, not pointer
int is_operator(char pattern) {
switch(pattern) {
case '.' :
return 1;
case '\' :
return 2;
case '+' :
return 3;
case '?' :
return 4;
default :
return 0;
}
}
int plus_modified(char *pattern) {
if(next_char(pattern) == '+')
return 1;
return 0;
}
int question_modified(char *pattern) {
if(next_char(pattern) == '?')
return 1;
return 0;
}
int escape_modified(char *pattern) {
if(prev_char(pattern) == '\')
return 1;
return 0;
}
/**
* You can use this recommended helper function
* Returns true if partial_line matches pattern, starting from
* the first char of partial_line.
*/
int matches_leading(char *line, char *pattern) {
//Check direct match
if(*line == *pattern && !is_operator(*pattern)) {
return 1;
}
//Check wildcard match
if(*pattern == '.' && !escape_modified(pattern)) {
return 1;
}
//Check escaped operator match
if(*line == *pattern && is_operator(*pattern) && escape_modified(pattern)) {
return 1;
}
//Check escape character
if(*pattern == '\')
return matches_leading(line, pattern + sizeof(char));
//Check for absent case of ? operator
if(question_modified(pattern))
return 1;
return 0;
}
/**
* You may assume that all strings are properly null terminated
* and will not overrun the buffer set by MAXSIZE
*
* Implementation of the rgrep matcher function
*/
int rgrep_matches(char *line, char *pattern) {
static int pattern_depth = 0;
//Base cases
if(*pattern == '') {
//Reset pattern for new line
if(*line == ' ') {
pattern -= pattern_depth * sizeof(char);
}
pattern_depth = 0;
return 1;
}
if(*line == '')
return 0;
//Reset pattern for new line
if(*line == ' ') {
pattern -= pattern_depth * sizeof(char);
pattern_depth -= pattern_depth;
return 0;
}
//Check for escape
if((*pattern == '\') && is_operator(next_char(pattern))) {
pattern += sizeof(char);
pattern_depth++;
}
//Check for match
if(matches_leading(line, pattern)) {
//For + modifier
if(plus_modified(pattern)) {
int chars_before = 1;
if(*pattern == *(pattern + 2 * sizeof(char)))
chars_before = 2;
//Go to next nonmatching character
//Stops one before because there is a line increment at the end of rgrep_matches
while(*(line + chars_before * sizeof(char)) == *pattern && !(*pattern == '.' && !escape_modified(pattern)))
line += sizeof(char);
//Handle .+
if(*pattern == '.' && escape_modified(pattern)) {
char wildcard = *line;
while(*(line + chars_before * sizeof(char)) == wildcard)
line += sizeof(char);
}
if(*pattern == '.' && !escape_modified(pattern)) {
//while(*(line + chars_before * sizeof(char)) != *(pattern + 2 * sizeof(char)))
while(!matches_leading(line + chars_before * sizeof(char), pattern + 2 * sizeof(char))){
line += sizeof(char);
if((*line == '' || *line == ' ') && *(pattern + 2 * sizeof(char)) != '')
return 0;
}
}
//Compensate for the character that the operator took
pattern += sizeof(char);
pattern_depth++;
}
//For ? modifier
if(question_modified(pattern)) {
//
if (*pattern == '.' && !escape_modified(pattern) && escape_modified(pattern + 3 * sizeof(char)) && *line == *(pattern + 3 * sizeof(char)) && *(line + sizeof(char)) != *(pattern + 3 * sizeof(char))) {
pattern_depth += 4;
return rgrep_matches(line + sizeof(char), pattern + 4 * sizeof(char));
}
//
else if(*pattern == '.' && !escape_modified(pattern) && *line == *(pattern + 2 * sizeof(char))) {
pattern_depth += 2;
return rgrep_matches(line, pattern + 2 * sizeof(char));
}
//
else if(*pattern == '.' && !escape_modified(pattern) && *line != *(pattern + 2 * sizeof(char))) {
pattern_depth += 2;
return rgrep_matches(line + sizeof(char), pattern + 2 * sizeof(char));
}
//
else if(*line == *pattern && *line == *(pattern + 2 * sizeof(char))) {
pattern_depth += 2;
return rgrep_matches(line, pattern + 2 * sizeof(char));
}
//
else if(*line == *pattern && next_char(line) == *(pattern + 2 * sizeof(char))){}
//
else if(*line == *pattern && next_char(line) != *(pattern + 2 * sizeof(char)) && *line != *(pattern + 2 * sizeof(char)))
{}//return 0;
//
else if(*line != *pattern && *line != *(pattern + 2 * sizeof(char)))
return 0;
//
else if(*line == *pattern && *pattern == '.' && escape_modified(pattern)){}
//
else if(!(*pattern == '.' && !escape_modified(pattern)) || *line != *pattern)
line -= sizeof(char);
//Compensate for the character that the operator took
pattern += sizeof(char);
pattern_depth++;
}
pattern += sizeof(char);
pattern_depth++;
}
//Reset the pattern on partial match so that we only get contiguous matches
else if(pattern_depth != 0 && *(pattern - pattern_depth * sizeof(char)) != '') {
pattern -= pattern_depth * sizeof(char);
pattern_depth -= pattern_depth;
}
//if(*line != ' ')
line += sizeof(char);
//Recurse
return rgrep_matches(line, pattern);
}
int main(int argc, char **argv) {
if (argc != 2) {
fprintf(stderr, "Usage: %s <PATTERN> ", argv[0]);
return 2;
}
/* we're not going to worry about long lines */
char buf[MAXSIZE];
while (!feof(stdin) && !ferror(stdin)) {
if (!fgets(buf, sizeof(buf), stdin)) {
break;
}
if (rgrep_matches(buf, argv[1])) {
fputs(buf, stdout);
fflush(stdout);
}
}
if (ferror(stdin)) {
perror(argv[0]);
return 1;
}
return 0;
}
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