printf 仿真

[q451157067]

需要一个类似于printf之类的函数.......可以接受随意参数 可以用 %s %d %f %ld占位符 ....
不知道怎么搞

[qq120848369]

找%号，然后走switch，从而在参数栈上怎么解析，之后做多少偏移。

[q451157067]

[Quote=引用 1 楼 qq120848369 的回复:]

找%号，然后走switch，从而在参数栈上怎么解析，之后做多少偏移。
[/Quote]
我也是这么想得.....有没有办法 直接用printf 的码 改

[q451157067]

[Quote=引用 1 楼 qq120848369 的回复:]

找%号，然后走switch，从而在参数栈上怎么解析，之后做多少偏移。
[/Quote]
我也是这么想得.....有没有办法 直接用printf 的码 改

[iamnobody]

首先要研究下这个：
http://wenku.baidu.com/view/03d73e0bf78a6529647d5329.html

要printf代码的话：

Purpose:
*       defines printf() - print formatted data
*
*******************************************************************************/

#include <cruntime.h>
#include <stdio.h>
#include <dbgint.h>
#include <stdarg.h>
#include <file2.h>
#include <internal.h>
#include <mtdll.h>
#include <stddef.h>
#include <process.h>

/***
*int printf(format, ...) - print formatted data
*
*Purpose:
*       Prints formatted data on stdout using the format string to
*       format data and getting as many arguments as called for
*       Uses temporary buffering to improve efficiency.
*       _output does the real work here
*
*Entry:
*       char *format - format string to control data format/number of arguments
*       followed by list of arguments, number and type controlled by
*       format string
*
*Exit:
*       returns number of characters printed
*
*Exceptions:
*
*******************************************************************************/

int __cdecl printf (
        const char *format,
        ...
        )
/*
 * stdout 'PRINT', 'F'ormatted
 */
{
    va_list arglist;
    int buffing;
    int retval;

    _VALIDATE_RETURN( (format != NULL), EINVAL, -1);

    va_start(arglist, format);

    _lock_str2(1, stdout);
    __try {
        buffing = _stbuf(stdout);

        retval = _output_l(stdout,format,NULL,arglist);

        _ftbuf(buffing, stdout);

    }
    __finally {
        _unlock_str2(1, stdout);
    }

    return(retval);
}

int __cdecl _printf_l (
        const char *format,
        _locale_t plocinfo,
        ...
        )
{
    va_list arglist;

    va_start(arglist, plocinfo);

    return _vprintf_l(format, plocinfo, arglist);
}


int __cdecl _printf_s_l (
        const char *format,
        _locale_t plocinfo,
        ...
        )
{
    va_list arglist;

    va_start(arglist, plocinfo);

    return _vprintf_s_l(format, plocinfo, arglist);
}

int __cdecl printf_s (
        const char *format,
        ...
        )
{
    va_list arglist;

    va_start(arglist, format);

    return _vprintf_s_l(format, NULL, arglist);
}

int __cdecl _printf_p_l (
        const char *format,
        _locale_t plocinfo,
        ...
        )
{
    va_list arglist;

    va_start(arglist, plocinfo);

    return _vprintf_p_l(format, plocinfo, arglist);
}

int __cdecl _printf_p (
        const char *format,
        ...
        )
{
    va_list arglist;

    va_start(arglist, format);

    return _vprintf_p_l(format, NULL, arglist);
}

static UINT_PTR __enable_percent_n = 0;

/***
*int _set_printf_count_output(int)
*
*Purpose:
*   Enables or disables %n format specifier for printf family functions
*
*Internals:
*   __enable_percent_n is set to (__security_cookie|1) for security reasons;
*   if set to a static value, an attacker could first modify __enable_percent_n
*   and then provide a malicious %n specifier.  The cookie is ORed with 1
*   because a zero cookie is a possibility.
******************************************************************************/
int __cdecl _set_printf_count_output(int value)
{
    int old = (__enable_percent_n == (__security_cookie | 1));
    __enable_percent_n = (value ? (__security_cookie | 1) : 0);
    return old;
}

/***
*int _get_printf_count_output()
*
*Purpose:
*   Checks whether %n format specifier for printf family functions is enabled
******************************************************************************/
int __cdecl _get_printf_count_output()
{
    return ( __enable_percent_n == (__security_cookie | 1));
}

[高性能架构探索]

楼主，其实最最简单的 你可以自己实现一个printf
但是你自己实现的要有以下功能：
一、支持同步异步
二、支持类型检查

同步异步可以通过 lock来实现，但是类型检查Windows不知道怎么来实现
倒是在Linux下，可以通过以下方式来做

inline int myprintf( const char *fmt, ... )
__attribute__ ((format (printf, 1, 2)));

[柯本]

对于可变参数,C与C++实现略有不同,而各个编译器实现也尽相同
好在一般的编译器都会提供printf的源码供参考,还有就是看编译器的文档都有介绍
对标准的C++,它有以下三个函数:
Header File

stdarg.h

Category

Variable Argument List Routines

Prototype

void va_start(va_list ap, lastfix);

type va_arg(va_list ap, type);

void va_end(va_list ap);

Description

Implement a variable argument list.

Some C functions, such as vfprintf and vprintf, take variable argument lists in addition to taking a number of fixed (known) parameters. The va_arg, va_end, and va_start macros provide a portable way to access these argument lists. They are used for stepping through a list of arguments when the called function does not know the number and types of the arguments being passed.

The header file stdarg.h declares one type (va_list) and three macros (va_start, va_arg, and va_end).

va_list: This array holds information needed by va_arg and va_end. When a called function takes a variable argument list, it declares a variable ap of type va_list.
va_start: This routine (implemented as a macro) sets ap to point to the first of the variable arguments being passed to the function. va_start must be used before the first call to va_arg or va_end.
va_start takes two parameters: ap and lastfix. (ap is explained under va_list in the preceding paragraph; lastfix is the name of the last fixed parameter being passed to the called function.)

va_arg: This routine (also implemented as a macro) expands to an expression that has the same type and value as the next argument being passed (one of the variable arguments). The variable ap to va_arg should be the same ap that va_start
initialized.

Note: Because of default promotions, you cannot use char, unsigned char, or float types with va_arg.

The first time va_arg is used, it returns the first argument in the list. Each successive time va_arg is used, it returns the next argument in the list. It does this by first dereferencing ap, and then incrementing ap to point to the following item. va_arg uses the type to both perform the dereference and to locate the following item. Each successive time va_arg is invoked, it modifies ap to point to the next argument in the list.

va_end: This macro helps the called function perform a normal return. va_end might modify ap in such a way that it cannot be used unless va_start is recalled. va_end should be called after va_arg has read all the arguments; failure to do so might cause strange, undefined behavior in your program.

Return Value

va_start and va_end return no values; va_arg returns the current argument in the list (the one that ap is pointing to).

[柯本]

晕,少打个关键字

而各个编译器实现也不尽相同

[q451157067]

[Quote=引用 4 楼 mingliang1212 的回复:]

首先要研究下这个：
http://wenku.baidu.com/view/03d73e0bf78a6529647d5329.html

要printf代码的话：
C/C++ code


Purpose:
* defines printf() - print formatted data
*
****************************************……
[/Quote]




谢过 你上面那个可变参数的解释 足够了....printf的就不看了...
我想的是 可以直接写出sql语句 这个的好像正好不行....% %是sql 的格式

SELECT * FROM `item` WHERE `name` LIKE '%XX%
如果我传递的 是 SELECT * FROM `item` WHERE `name` LIKE '%%s%‘ ,s
正好悲剧

[iamnobody]

[Quote=引用 8 楼 q451157067 的回复:]

谢过 你上面那个可变参数的解释 足够了....printf的就不看了...
我想的是 可以直接写出sql语句 这个的好像正好不行....% %是sql 的格式

SELECT * FROM `item` WHERE `name` LIKE '%XX%
如果我传递的 是 SELECT * FROM `item` WHERE `name` LIKE '%%s%‘ ,s
正好悲剧
[/Quote]

扫了一眼printf调用的那个2000行左右的函数。。。也就是分析格式控制符“%d"之类的那个函数。头都大了。。。
现在才发现stl里的__Name__Something__ 之类的__ 多么的可爱。至少还可以勉强看得明白，但是这个c语言。。。里面一大堆的 abc 2000行啊。。

[柯本]

SQL的参数,又是各个数据库的SQL语言各不相同,参考下你用数据库的SQL手册

[q451157067]

[Quote=引用 9 楼 mingliang1212 的回复:]

引用 8 楼 q451157067 的回复:

谢过 你上面那个可变参数的解释 足够了....printf的就不看了...
我想的是 可以直接写出sql语句 这个的好像正好不行....% %是sql 的格式

SELECT * FROM `item` WHERE `name` LIKE '%XX%
如果我传递的 是 SELECT * FROM `item` WHERE `name` ……
[/Quote]

额 我都搞定了...

不过C的 库 确实看的头疼...和STL比 他确实复杂了太多...不过STL好像也借用了C++的库吧...貌似有吧....
貌似 C++的底层的也是那样复杂吧~~~