cstdarg可变参数列表

va_list

Type to holdinformation about variable arguments

This type is used as a parameter for the macros definedin cstdarg to retrieve the additional arguments of a function.

类型va_list用于检索函数中附加的参数，作为定义在cstdarg中的宏的参数使用。

Each compiler may implement this type in its own way. Itis only intended to be used as the type for the object used as first argumentfor theva_start, va_arg and va_endmacros.

va_startis in charge of initializing an object of this type, so that subsequent callstova_arg with it retrieve the additional arguments passed tothe function.

       每个编译器都会使用它自己的方式实现这个类型。我们只需要把它作为一种类型用于va_start, va_arg, va_end的第一个参数。Va_start负责初始化这种类型的一个对象，之后由va_arg负责检索传给函数的其它附加参数。

Before a function that has initialized a va_listobject with va_start returns, theva_endshall be executed.

在一个函数利用va_start初始化va_list对象后，va_end应当初执行。

 

va_start

void va_start ( va_list ap, paramN );

Initialize a variable argument list: 初始化一个变量参数列表

Initializes the objectof type va_list passed asargumentap to hold the information needed to retrieve the additionalarguments after parameterparamN with function va_arg.

初始化作为参数ap传入的类型为va_list的对象，这个对象将用于函数va_arg中检索在参数paramN后的附加参数的信息。

 A function that executes va_start, shall also executeva_end before it returns.

一个执行va_start的函数也应该在返回前执行va_end。

Parameters

ap： Object of type va_list that will hold theinformation needed to retrieve the additional arguments withva_arg.

paramN： Parametername of the last named parameter in the function definition.

函数定义中最后一个参数的参数名。

 

 

/* va_start example */#include <stdio.h>#include <stdarg.h>void PrintFloats ( int amount, ...){  int i;  double val;  printf ("Floats passed: ");  va_list vl;  va_start(vl,amount);  for (i=0;i<amount;i++)  {    val=va_arg(vl,double);    printf ("\t%.2f",val);  }  va_end(vl);  printf ("\n");}int main (){  PrintFloats (3,3.14159,2.71828,1.41421);  return 0;}

/* va_arg example */#include <stdio.h>#include <stdarg.h>int FindMax ( int amount, ...){  int i,val,greater;  va_list vl;  va_start(vl,amount);  greater=va_arg(vl,int);  for (i=1;i<amount;i++)  {    val=va_arg(vl,int);    greater=(greater>val)?greater:val;  }  va_end(vl);  return greater;}int main (){  int m;  m= FindMax (7,702,422,631,834,892,104,772);  printf ("The greatest one is: %d\n",m);  return 0;}

/* va_arg example */#include <stdio.h>#include <stdarg.h>void PrintLines ( char* first, ...){  char* str;  va_list vl;  str=first;  va_start(vl,first);  do {    printf ("%s\n",str);    str=va_arg(vl,char*);  } while (str!=NULL);  va_end(vl);}int main (){  PrintLines ("First","Second","Third","Fourth",NULL);  return 0;}