如何在包装函数调用的顺序中正确使用va_list? [英] How to use va_list correctly in a sequence of wrapper functions calls?
问题描述
库在调试输出函数中使用va_list(在stdarg.h中定义的arg数组宏的标准指针):
void __debug__(const char * fmt,...)
{
va_list args;
va_start(args,fmt);
vprintf(fmt,args);
va_end(args);
}
然而,vprintf将数据发送到不正确的流,我需要重定向库的调试输出纠正串口。
库具有.c配置文件,我编写c ++代码,所以我使用包装函数指针从c代码调用c ++样式代码。所以我重写这个函数:
extern void(* printDebugMsg)(const char * fmt,...);
void __debug__(const char * fmt,...)
{
va_list args;
printDebugMsg(fmt,args);
}
其他cpp文件:
void printDebugMsgImplementation(const char * fmt,...)
{
va_list args;
char buffer [100] = {0};
sprintf(buffer,fmt,args);
debugUart-> write(buffer);
}
void(* printDebugMsg)(const char * fmt,...)=& printDebugMsgImplementation;
结果调试输出如下所示:
TCP:Init 0 Sockets
IP:Src。 IP:0.0.14.1668436768
ETH:Dest.MAC:A1E05E10:A0002B44:5F9F:01:5FF8:33
文本和一些数字(如0)似乎是正确的,但大多数其他数字似乎格式错误(但也可能是内部库问题)。
我试图使用va_list重写我的代码,通常是在例子中进行的:
void __debug__(const char * fmt,...)
{
va_list args;
va_start(args,fmt);
printDebugMsg(fmt,args);
va_end(args);
}
和.cpp文件:
void printDebugMsgImplementation(const char * fmt,...)
{
va_list args;
char buffer [100] = {0};
va_start(args,fmt);
vsprintf(buffer,fmt,args);
va_end(args);
debugUart-> write(buffer);
}
然而结果更糟糕的是:
TCP:Init -1579131344套接字
ARP:Dest.IP:-1579131400.-1610601474.24805.4
ARP:Src.MAC :A1E05DF8:A0002BFE:60FF:04:616C:20
我做错了什么?在我的包装函数调用的情况下如何处理va_list?
你不能通过 va_list
到一个期望 ...
的函数,除非该函数(当然)期望 va_list
在变量参数部分。您的代码显然不会。
您需要明确接受 va_list
参数到 printDebugMsg ()
,因为那是你所经历的。参见例如 vprintf()
它解决了 printf()
家族的这个问题。
I have an ethernet library for microcontroller (keil rl-tcpnet for lpc2478). Library uses va_list (standard pointer to arg array macro defined in stdarg.h) in debug output function in such a way:
void __debug__ (const char *fmt, ...)
{
va_list args;
va_start (args,fmt);
vprintf (fmt,args);
va_end (args);
}
However vprintf sends data to incorrect stream and I need to redirect debug output of library to correct serial port. Library has .c cofigure files and I write c++ code so I use wrapper function pointers to call c++ style code from c code. So I rewrite this function:
extern void (* printDebugMsg)(const char * fmt, ...);
void __debug__ (const char *fmt, ...)
{
va_list args;
printDebugMsg(fmt, args);
}
other cpp file:
void printDebugMsgImplementation(const char * fmt, ...)
{
va_list args;
char buffer[100] = { 0 };
sprintf(buffer, fmt, args);
debugUart->write(buffer);
}
void (* printDebugMsg)(const char * fmt, ...) = &printDebugMsgImplementation;
The result debug output looks like:
TCP: Init 0 Sockets
IP : Src. IP : 0.0.14.1668436768
ETH: Dest.MAC: A1E05E10:A0002B44:5F9F:01:5FF8:33
The text and some numbers (like 0) seems to be correct but most other ones seems to be wrongly formatted (however it can be internal library problem also). I tried to rewrite my code using va_list as it is usually made in examples:
void __debug__ (const char *fmt, ...)
{
va_list args;
va_start (args,fmt);
printDebugMsg(fmt, args);
va_end (args);
}
and .cpp file:
void printDebugMsgImplementation(const char * fmt, ...)
{
va_list args;
char buffer[100] = { 0 };
va_start(args, fmt);
vsprintf(buffer, fmt, args);
va_end(args);
debugUart->write(buffer);
}
However the result is definetely worse that it was:
TCP: Init -1579131344 Sockets
ARP: Dest.IP: -1579131400.-1610601474.24805.4
ARP: Src.MAC: A1E05DF8:A0002BFE:60FF:04:616C:20
What I'm doing wrong? And how to deal with va_list in my case of wrapper functions calls?
You can't pass va_list
to a function expecting ...
, unless that function (of course) expects a va_list
in the variable-arguments part. Your code clearly does not.
You need to explicitly accept a va_list
argument into printDebugMsg()
, since that's what you're passing. See for instance vprintf()
which solves this problem for the printf()
family.
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