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cvargcal
Joined: 17 Feb 2015
Posts: 134
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| error compiler with symbol "_" |
 Posted: Sat Apr 18, 2020 10:46 am |
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Hi, I try make portable a code from mplabx, but i get error with the simbol "_"
why?
for example
| Code: | uint8_t* AddStringToBuf(uint8_t *_buf, char *_string)
{
uint16_t _length = strlen(_string);
_buf[0] = _length >> 8;
_buf[1] = _length & 0xFF;
_buf+=2;
strncpy((char *)_buf, _string, _length);
return _buf + _length;
} |
this operation strlen(_string) make error if i write the varible with _
So some variable i shoud be declare without "_"
| Code: | uint8_t* AddStringToBuf(uint8_t *_buf, char *string)
{
uint16_t _length = strlen(string);
_buf[0] = _length >> 8;
_buf[1] = _length & 0xFF;
_buf+=2;
strncpy((char *)_buf, string, _length);
return _buf + _length;
} |
The code work fine... but to end i have rename the variables.
maybe its stupid, but i want know why happen this.
Thanks |
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temtronic
Joined: 01 Jul 2010
Posts: 9244
Location: Greensville,Ontario
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| Posted: Sat Apr 18, 2020 11:02 am |
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might be a 'C' syntax that variables MUST begin with a LETTER.....
CCS C mostly follows K&R C, though I've never been formally taught any C....
the pros here WILL know....
To me using an 'underscroe' character is bad...too hard to see on a screen using my 67 year old eyeballs.... |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19541
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| Posted: Sat Apr 18, 2020 11:23 am |
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C has restrictions on the use of _.
| Quote: |
predefined macro names shall begin with a leading underscore followed by an uppercase letter or a second underscore.”
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By avoiding leading underscores in your identifiers, you avoid the possibility of your identifier conflicting with a predefined symbol defined by the compiler implementation. Depending on the context, conflicts like this can be difficult to diagnose, so completely avoiding the possibility of a conflict is a good practice.
Coding standards and/or style guides within an organization will often prohibit leading underscores (to avoid the conflicts discussed above), and sometimes establish a naming convention for various types of identifiers, including whether or not to use underscores to separate words.
Because CCS by default does not use case, you have to avoid _ as the
leading character. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sat Apr 18, 2020 12:10 pm |
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temtronic, remember that K&R pdf I showed you how to get the other day ?
It's in there. Search for the word: underscore
See section: 2.1 Variable Names |
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cvargcal
Joined: 17 Feb 2015
Posts: 134
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| Posted: Sat Apr 18, 2020 12:15 pm |
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I like this answers...
Thanks you! |
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jeremiah
Joined: 20 Jul 2010
Posts: 1355
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| Posted: Sat Apr 18, 2020 1:07 pm |
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7.1.3 of the standard also has:
| Quote: |
— All identifiers that begin with an underscore and either an uppercase letter or another underscore are always reserved for any use.
— All identifiers that begin with an underscore are always reserved for use as identifiers with file scope in both the ordinary and tag name spaces.
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So as Ttelmah alluded to, using the _ at the beginning of an identifier (macro, variable, function, etc.) is technically "undefined", as defined in the standard:
| Quote: |
If the program declares or defines an identifier in a context in which it is reserved (other than as allowed by 7.1.4), or defines a reserved identifier as a macro name, the behavior is undefined.
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temtronic
Joined: 01 Jul 2010
Posts: 9244
Location: Greensville,Ontario
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| Posted: Sat Apr 18, 2020 3:13 pm |
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heck, I downloaded it, got to read about 3 pages, then everyone wanted THEIR stuff done....I did run the plow through the 1/2 ac garden once, hauled a 70' black walnut tree home in pieces, lots of pieces.Only 3 pieces left, easch about 3200# and at top of steep hill....sigh.
full 16 hr days are getting 'challenging', at 67 I get tired for some silly reason. |
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