search for char sequences in C within a loop - c

Question

I am trying to find the most efficient way to find tags in a given char array. These "tags" are a sequence of chars located randomly within a char array.
Here is an example: given a char array: {'a','s','s','1','m','s','g','e','x','x','r','s','1',...}. the tag "ss1" indicates the beginning of a message which contains every char until a sequence of "exx" is found, which a tag for the end of the message, and it keeps searching the array for the next sequence of "s1". In this example, the message here is "msg".
my initial design was (pseudo code)
while(array[i] != '\0')
if(array[i] == 's' && array[i+1] == 's' && array[i+2] == '1' )
int j = i+3;
if(array[j] != '\0' && array[j] == 'e' && array[j+1] == 'x' && array[j+2] == 'x' )
i += 3;
else
print(array[j]);
else i++; //next char
may be a little flawed, but you get the idea. Is there a better way? i thought about strstr but since I'm dealing with a char array here and still looping even after deciphering a message, I thought it might be difficult to implement.

Answer 1

Try to maintain a state denoting how much of the tag start and end you have found. Something like this: (This code will work even if the message within the tag is of arbitrary length)
int state = 0;
int found = 0;
int i = 0,j;
int msgStartIndex;
int msgEndIndex;
while(array[i]){
if((array[i] == 's' && state == 0) || (array[i] == 's' && state == 1) || (array[i] == '1' && state == 2) ){
state++;
if(!found && state == 3){
msgStartIndex = i+1;
found = 1;
}
}
else if(!found && (array[i] = 's' && state == 2))
state = 2;
else if(!found)
state = 0;
if((array[i] == 'e' && state == 3) || (array[i] == 'x' && state == 2) || (array[i] == 'x' && state == 1) ){
state--;
if(found && state == 0){
found = 0;
msgEndIndex = i-3;
for(j=msgStartIndex; j < msgEndIndex+1; j++)
printf("%c",array[j]);
printf("\n");
}
}
else if(found && (array[i] == 'e') && (state == 2 || state == 1))
state = 2;
else if(found)
state = 3;
i++;
}
Updated answer for start tag st1 and end tag ex1
int state = 0;
int found = 0;
int i=0,j;
int msgStartIndex;
int msgEndIndex;
while(array[i]){
if((array[i] == 's' && state == 0) || (array[i] == 't' && state == 1) || (array[i] == '1' && state == 2) ){
state++;
if(!found && state == 3){
msgStartIndex = i+1;
found = 1;
}
}
else if(!found && (array[i] = 's' && (state == 1 || state == 2)))
state = 1;
else if(!found)
state = 0;
if((array[i] == 'e' && state == 3) || (array[i] == 'x' && state == 2) || (array[i] == '1' && state == 1) ){
state--;
if(found && state == 0){
found = 0;
msgEndIndex = i-3;
for(j=msgStartIndex; j < msgEndIndex+1; j++)
printf("%c",array[j]);
printf("\n");
}
}
else if(found && (array[i] == 'e') && (state == 2 || state == 1))
state = 2;
else if(found)
state = 3;
i++;