[2010-01] goofing around with string substitution

strsub.c

//&>/dev/null;x="${0%.*}";[ ! "$x" -ot "$0" ]||(rm -f "$x";cc -o "$x" "$0")&&"$x" $*;exit

#import <stdio.h>
#import <stdlib.h>
#import <string.h>

typedef struct strpart {
	char* start;
	int len;
	struct strpart* next;
} strpart;

strpart* new_strpart(char* start, int len) {
	strpart* new = malloc(sizeof(strpart));
	
	new->start = start;
	new->len = len;
	new->next = NULL;
	
	return(new);
}

// Given the tail of a strpart list, adds an element and returns the
// new tail address.
strpart* strpart_append(strpart* tail, char* start, int len) {
	strpart* new_tail = new_strpart(start, len);
	
	tail->next = new_tail;
	
	return new_tail;
}

char* strpart_compile(strpart* head) {
	int len_result = 0;
	char* result;
	strpart* current;
	
	for(current = head; current; current = current->next) {
		len_result += current->len;
		current = current->next;
	}
	
	result = malloc(sizeof(char) * len_result + 1);
	
	int result_index = 0;
	int current_index = 0;
	
	for(current = head; current; current = current->next) {
		for(current_index = 0; current_index < current->len; current_index++) {
			result[result_index++] = current->start[current_index];
		}
	}
	
	result[result_index] = '\x00';
	
	return(result);
}

void strpart_free(strpart* head) {
	strpart* current;
	strpart* next;
	
	for(current = head; current; current = current->next) {
		next = current->next;
		free(current);
		current = next;
	}
}

char* strsub(char* subject, char* old, char* new) {
	int len_subject = strlen(subject);
	int len_old = strlen(old);
	int len_new = strlen(new);
	
	strpart* head = new_strpart(NULL, 0);
	strpart* tail = head;
	
	int index_subject;
	int index_old;
	int index_added = 0;
	
	for(index_subject = 0; index_subject < len_subject;) {
		for(index_old = 0; index_old < len_old &&
		                   index_old + index_subject < len_subject &&
		                   old[index_old]; index_old++);
		
		printf("subject/added = %i/%i\n", index_subject, index_added);
		printf("head->next = %p\n", head->next);
		printf("%s\n", strpart_compile(head));
		
		if(index_old == len_old) {
			if(index_added < index_subject - 1) {
				tail = strpart_append(tail, &subject[index_added + 1], index_subject - index_added);
			}
			
			tail = strpart_append(tail, new, len_new);
			
			index_added = index_subject = index_subject + len_old;
		} else {
			index_subject++;
		}
	}
	
	if(index_added < index_subject - 1) {
		tail = strpart_append(tail, &subject[index_added + 1], index_subject - index_added);
	}
	
	char* result = strpart_compile(head);
	
	strpart_free(head);
	
	return(result);
}

int main(int argc, char* argv[]) {
	printf("%s\n", strsub("Ha ha ham ha!", "ham", "pork"));
	
	return 0;
}