Question

If I have an arithmetic expression like x+y-12 / z in a string (c-style or otherwise) in c or c++, how can I extract one item at a time (including the operator)? There may or may not be a space in the expression and multiple digits are allowed for constants.

Answer 1

If your input is simple you can start with something like this:

typedef struct token {
  int type;
  int ival;
  char sval[256];
  int  ssize;
} Token;

char *get_next_tok(char *buffer, Token *token) {
  char *p = buffer; while (isspace(*p)) p++; // trim
  if (my_isopchar(*p))     // checks -+*...
   p=my_get_op(p, token);  // a function to handle multi-char ops
  else if (isdigit(*p)) {
   token->ival=strtol(p, &p, 10);
   token->type=TK_CONST;
  }
  else if (isalpha(*p)) {
   while (isalpha(*p)) {
     token->sval[token->ssize++] = *p; p++;
   }
   token->type = TK_VAR;
  }
  return p;
}