在弹性词法分析器中与“ if”匹配

Question

I am trying to write a piece of code in flex that matches the "if" keyword. When I write:

if printf("Saw an if");

it matches but it also matches, for example if the input is abcdifcd , output becomes abcdSaw an ifcd , but I want to be invalid, ie the output must be abcifcd since it is invalid. In other words, I want it to be valid only if the keyword "if" is found alone, for example I want if abcd or abcd if to be valid but ifa, aif etc. to be invalid. How can I do this?

Answer 1

You need to add a rule which matches "words", whatever you consider them to be. Remember to put the rule for "if" first. For example:

"if"         printf("Saw a if");
[a-zA-Z]+    ECHO