How to perform other operations when my tokenizer recognizes a token? - c++

Question

I have written a simple tokenizer that will split a command line into seperate lines each containing a single word. I am trying to ...
Make the program close if the first word of a command line is "quit"
Recognize instructions such as "Pickup", "Save", and "Go" in which the compiler will then look to the next token.
My idea has been to use a simple switch with cases to check for these commands, but I cannot figure out where to place it.
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
char command[256];
int commandIndex;
char token[32];
int isWhiteSpace(char character) {
if (character == ' ') {
return 1;
}
else if(character == '\t') {
return 1;
}
else if(character < ' ') {
return 1;
}
else {
return 0;
}
} char* getToken() {
int index = 0; // Skip white spaces
while(commandIndex<256 && isWhiteSpace(command[commandIndex])) {
commandIndex ++;
} // If at end of line return empty token
if(commandIndex>=256) {
token[0] = 0;
return token;
} // Capture token
while(commandIndex<256 && !isWhiteSpace(command[commandIndex])) {
token[index] = command[commandIndex];
index++;
commandIndex ++;
}
token[index] = 0;
return token;
}
void main() {
printf("Zeta - Version 2.0\n");
while(1) {
printf("Command: ");
gets_s(command);
commandIndex = 0;
char* token = getToken();
while (strcmp(token,"") != 0) {
printf("%s\n", token);
token = getToken();
}
}
}

Answer 1

A little reorganization of the loop you have in main will do it.
int main() {
printf("Zeta - Version 2.0\n");
bool done = false;
while (!done) {
printf("Command: ");
gets_s(command);
commandIndex = 0;
char* token = getToken();
if (strcmp(token, "quit") == 0) {
done = true;
} else if (strcmp(token, "pickup") == 0) {
doPickup();
} else if (strcmp(token, "save") == 0) {
char * filename = getToken();
doSave(filename);
} ...
}
return 0;
}
You can't use a switch statement with strings, so you just use a bunch of if ... else if ... statements to check for each command. There are other approaches, but this one required the fewest changes from the code you already have.
In the example, under the handling for "save" I showed how you can just call getToken again to get the next token on the same command line.
(Note that I also fixed the return value for main. Some compilers will let you use void, but that's not standard so it's best if you don't do that.)