I'm trying to write a program (a minicompiler) in which I can have multiple commands such as "write", "repeat", "stop" (which signifies the end of a repeat command) and some expressions (ex: a = n * b +/- ...).
For some reason, when using strtok to take out each element out of the expression line (where the line is c = a + b), I get null when trying to get the next element (which should be '='). Anyone know why this happens?
#strtok returns null even though there still are substrings not containing the separator
junior bramble
still oxideBOT
mighty pivot
can we see the code?
junior bramble
```int var1 = word2[0] - 'a';
word2 = strtok(NULL, " "); /// =
...
the issue is here, word2 returns null instead of '=' after calling strtok
this is just the repeat function, by the way, but its the same code as in the main function, since I need it to repeat the lines [from, to]
chilly sparrow
What's the input?
junior bramble
INCEPE
a = 1
b = a
SCRIE a
SCRIE b
REPETA 10
c = a + b
a = b
b = c
SCRIE c
STOP
STOP
INCEPE means the start of the program
SCRIE <var> means write var
REPETA <n> is repeat n times the lines between repeat and stop
but when doing the expression c = a + b, strtok only gives me c, then returns null
chilly sparrow
int var1 = word2[0] - 'a';
What is the value ofword2when the program is at this line?
junior bramble
> `int var1 = word2[0] - 'a';`
What is the value of `word2` when the program is ...
c
first, word2 = strtok(line[i], " ")
line[i] is c = a + b
chilly sparrow
So you did look into the value of word2 right?
junior bramble
So you did look into the value of `word2` right?
yes, it is c at first
chilly sparrow
Try checking the string word2 + 2 at that moment.
junior bramble
but then, when doing word2 = strtok(NULL, " "), I expect it to be =
it's "="
but shouldn't "word2 = strtok(NULL, " ")" work?
chilly sparrow
I'm seeing something abnormal there. The rest of the line should be = a + b.
Just realized this is C++ also, you should not use NULL but rather nullptr.
Check the contents of line[i] at the beginning of the loop iteration.
junior bramble
I'm seeing something abnormal there. The rest of the line should be `= a + b`.
word2 only gets the substring up until space, but line[i] (the whole string) is "c = a + b"
chilly sparrow
That doesn't look like the beginning of the loop iteration.
junior bramble
Just realized this is C++ also, you should not use `NULL` but rather `nullptr`.
oh, I'll fix that, but I don't think thats the issue though
junior bramble
That doesn't look like the beginning of the loop iteration.
what do you mean
chilly sparrow
It's not the issue indeed, just a reminder about more proper C++ code.
chilly sparrow
what do you mean
Check line[i] when the program is at the beginning of the loop iteration.
I.e. on the line of word2 = strtok(line[i], " ");.
junior bramble
it's c = a + b
chilly sparrow
Those are not spaces.
junior bramble
Those are not spaces.
Oh
chilly sparrow
Looks like the string has already been trampled on using strtok before that.
junior bramble
in the main loop, I get the line with cin.getline
junior bramble
Looks like the string has already been trampled on using `strtok` before that.
You can't use strtok on the same string multiple times?
this is the main loop
chilly sparrow
You can't use strtok on the same string multiple times?
Indeed, as it modifies the string.
junior bramble
Indeed, as it modifies the string.
oh, so should I just copy the string in another array with strcmp and then use strtok on that array?
so that I don't lose the string when using strtok
chilly sparrow
Yes.
junior bramble
Oh, thank you!
chilly sparrow
But you should probably just use std::string and its functions.
Are you made use C strings?
junior bramble
Are you made use C strings?
no, but I'm not really familiar with using std::string
chilly sparrow
Then probably a good time to learn about it.
junior bramble
Then probably a good time to learn about it.
Yes, anyway, thank you for your help!
!solved