C++の関数引数リスト内の末尾のドット（...）

Question

Doxygenのドキュメントとともに以下に示すように、好奇心を感じる関数を見つけたときにいくつかの解析を実行するC++ソースコードファイルを探していました。

私の質問は、関数ERRORの引数で、末尾のドット（...）は何ですか？ はどういう意味ですか？これが初めて使用されているのがわかります。私が使用

/** 
* Create an error with given message id and fill in given string in message 
* @PARAM row row where the error occured (0 to neglect) 
* @PARAM col column where the error occured (0 to neglect) 
* @PARAM id id of the message 
* @PARAM arg an argument which will be filled in in the message, 
*    replacing %s, %i, %f, %c 
*/ 
Error::Error(const int row, const int col, const int id, ...) 
: err_row(row), err_col(col), err_id(id) 
{ 
    //sprintf(msg, msgdesc(id)); 
    const char* msg_desc = msgdesc(id); 

    va_list args; 
    va_start(args, msg_desc); 
    vsnprintf(msg, sizeof(msg)-1, msg_desc, args); 
    msg[sizeof(msg)-1] = '\0'; 
    va_end(args); 
} 

gccコンパイラが私をスロー可変長引数リストをある

parser_error.cpp: In constructor ‘Error::Error(int, int, int, ...)’: 
parser_error.cpp:30: warning: second parameter of ‘va_start’ not last named argument 

Answer 1

（他のファイルに関する他の人の間で）警告以下。男性からstdarg：

NAME 
    stdarg -- variable argument lists 

SYNOPSIS 
    #include <stdarg.h> 

    void 
    va_start(va_list ap, last); 

    type 
    va_arg(va_list ap, type); 

    void 
    va_copy(va_list dest, va_list src); 

    void 
    va_end(va_list ap); 

DESCRIPTION 
    A function may be called with a varying number of arguments of varying types. The include file <stdarg.h> declares a 
    type (va_list) and defines three macros for stepping through a list of arguments whose number and types are not known to 
    the called function. 

    The called function must declare an object of type va_list which is used by the macros va_start(), va_arg(), va_copy(), 
    and va_end(). 

    The va_start() macro must be called first, and it initializes ap, which can be passed to va_arg() for each argument to be 
    processed. Calling va_end() signals that there are no further arguments, and causes ap to be invalidated. Note that 
    each call to va_start() must be matched by a call to va_end(), from within the same function. 

    The parameter last is the name of the last parameter before the variable argument list, i.e., the last parameter of which 
    the calling function knows the type. 

    Because the address of this parameter is used in the va_start() macro, it should not be declared as a register variable, 
    or as a function or an array type. 

    The va_arg() macro expands to an expression that has the type and value of the next argument in the call. The parameter 
    ap is the va_list ap initialized by va_start(). Each call to va_arg() modifies ap so that the next call returns the next 
    argument. The parameter type is a type name specified so that the type of a pointer to an object that has the specified 
    type can be obtained simply by adding a * to type. 

    If there is no next argument, or if type is not compatible with the type of the actual next argument (as promoted accord- 
    ing to the default argument promotions), random errors will occur. 

    The first use of the va_arg() macro after that of the va_start() macro returns the argument after last. Successive invo- 
    cations return the values of the remaining arguments. 

    The va_copy() macro copies the state of the variable argument list, src, previously initialized by va_start(), to the 
    variable argument list, dest, which must not have been previously initialized by va_start(), without an intervening call 
    to va_end(). The state preserved in dest is equivalent to calling va_start() and va_arg() on dest in the same way as was 
    used on src. The copied variable argument list can subsequently be passed to va_arg(), and must finally be passed to 
    va_end() when through with it. 

    After a variable argument list is invalidated by va_end(), it can be reinitialized with va_start() or made a copy of 
    another variable argument list with va_copy(). 

EXAMPLES 
    The function foo takes a string of format characters and prints out the argument associated with each format character 
    based on the type. 

      void foo(char *fmt, ...) 
      { 
        va_list ap, ap2; 
        int d; 
        char c, *s; 

        va_start(ap, fmt); 
        va_copy(ap2, ap); 
        while (*fmt) 
          switch(*fmt++) { 
          case 's':      /* string */ 
            s = va_arg(ap, char *); 
            printf("string %s\n", s); 
            break; 
          case 'd':      /* int */ 
            d = va_arg(ap, int); 
            printf("int %d\n", d); 
            break; 
          case 'c':      /* char */ 
            /* Note: char is promoted to int. */ 
            c = va_arg(ap, int); 
            printf("char %c\n", c); 
            break; 
          } 
        va_end(ap); 
        ... 
        /* use ap2 to iterate over the arguments again */ 
        ... 
        va_end(ap2); 
      } 

COMPATIBILITY 
    These macros are not compatible with the historic macros they replace. A backward compatible version can be found in the 
    include file <varargs.h>. 

STANDARDS 
    The va_start(), va_arg(), va_copy(), and va_end() macros conform to ISO/IEC 9899:1999 (``ISO C99''). 

BUGS 
    Unlike the varargs macros, the stdarg macros do not permit programmers to code a function with no fixed arguments. This 
    problem generates work mainly when converting varargs code to stdarg code, but it also creates difficulties for variadic 
    functions that wish to pass all of their arguments on to a function that takes a va_list argument, such as vfprintf(3). 

Answer 2

これは可変長引数リストです。この関数は、基本的にユーザーに最低3つの引数（row、col、id）を渡す必要がありますが、より多くの引数を渡すことができます。追加の引数は、va_list/va_start/va_endコードで処理されます。