Acceptable use of a label and 'goto'? [closed] - c++

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I am writing a tokenizer for a compiler. I have a while loop that loops over characters and then a switch that checks for certain conditions. I then need to exit both blocks to write the token:
Token token;
while (peekChar() != '\0')
{
switch (c = nextChar())
{
case '(':
token = Token(TOKEN_LEFT_PAREN, currentLine);
goto MakeToken;
// ... every other character, some with lots of logic
}
}
MakeToken:
// write the token
Is this an acceptable use of labels, or is there a better way? I have learnt to think of labels as just terrible practice, but surely there must be uses for them (or they wouldn't be implemented in the standard?). Thanks.

Answer 1

Generally, when we want to break several scopes at once, it means that we can make sub-functions; Something like:
bool HandleChar(char c)
{
switch (c)
{
case '(': {
Token token = Token(TOKEN_LEFT_PAREN, currentLine);
return true;
}
// ... every other character, some with lots of logic
}
}
And then:
while (peekChar() != '\0')
{
if (HandleChar(nextChar())) {
break;
}
}
// ...

Answer 2

You could implement the very same with break here, without needing to use goto.
The only time I found a only-slightly-revolting case of goto in C++ was in a complex state machine where developers took arduous care not to mess up local state.
Generally, a parser (or more specifically, a tokenizer) is the last place where I'd go for spaghetti coding -- if anything, this calls for using C++ in a more functional way.

Answer 3

I believe this is one of very few examples when goto is accepted however you could use a flag:
Token token;
bool flag = true;
while ((peekChar() != '\0') && flag)
{
switch (c = nextChar())
{
case '(':
token = Token(TOKEN_LEFT_PAREN, currentLine);
flag = false;
// ... every other character, some with lots of logic
}
}