comma operator clarification

This is a discussion on comma operator clarification within the C Programming forums, part of the General Programming Boards category; Hi, i was writing a program and i suddenly declared like this Code: int i,char c; it gave an error ...

  1. #1
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    comma operator clarification

    Hi,

    i was writing a program and i suddenly declared like this
    Code:
    int i,char c;
    it gave an error and then i declared like this
    Code:
    int i,int j;
    it still gave me an error. Could some one please point out to me the rule in the draft that makes it to give error, so that i can remember or apply it properly to some other cases.

    Thanks and regards,
    satya

  2. #2
    Programming Wraith GReaper's Avatar
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    You can't declare more than one type in the same statement. If the variables are of the same type, just separate them by commas. If the variables are of different type, declare them in separate statements, like:
    Code:
    int i;
    char c;
    and
    Code:
    int i, j;
    Devoted my life to programming...

  3. #3
    Registered User Hodor's Avatar
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    Quote Originally Posted by Satya View Post
    Hi,
    Could some one please point out to me the rule in the draft that makes it to give error, so that i can remember or apply it properly to some other cases.
    satya
    That's not a use of the comma operator. The section of the standard[1] you should be looking at is 6.7.5 (particularly 6.7.5p6)


    [1] ISO/IEC 9899:201x Committee Draft April 12, 2011 N1570

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    Quote Originally Posted by GReaper View Post
    You can't declare more than one type in the same statement.
    That's not true. A compound statement (which is what you get when you place a bunch of declarations and statements within curly braces to form a block) can contain multiple declarations (of both types and variables) as well as other statements. Most other statements can't include any declarations.

    In any event.....

    I don't have a copy of the 2011 standard handy, but the relevant section of the 1999 standard is 6.7. As Hodor said, this is not a usage of the comma operator. Declarations are composed of a single declaration specifier (which specifies types, storage class, etc) and a list of one or more declarators separated by commas (where each declarator includes an identifier - the name of something being declared).

    In a declaration
    Code:
        int i, j;
    the "int" is the declaration specifier, and i and j are both the names of things being declared (i.e. the declarators).

    Whereas, the (incorrect) declaration
    Code:
        int i, char c;
    is invalid because "int" and "char" are both declaration specifiers.
    Right 98% of the time, and don't care about the other 3%.

    If I seem grumpy or unhelpful in reply to you, or tell you you need to demonstrate more effort before you can expect help, it is likely you deserve it. Suck it up, Sunshine, and read this, this, and this before posting again.

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    Programming Wraith GReaper's Avatar
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    Quote Originally Posted by grumpy View Post
    That's not true. A compound statement (which is what you get when you place a bunch of declarations and statements within curly braces to form a block) can contain multiple declarations (of both types and variables) as well as other statements. Most other statements can't include any declarations
    Oh, I see! I didn't have compound statements in mind, though.
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