用C语言模仿Python函数的一种简单实现方法

系统 437 0

首先得说明一点,C 语言不是函数式编程语言,要想进行完全的函数式编程,还得先写个虚拟机,然后再写个解释器才行(相当于 CPython )。

下面我们提供一个例子,说明 C 语言函数可以“适度地模仿” Python 函数。

我们有如下的 Python 程序:

            
def line_conf(a, b):
  def line(x):
    return a*x + b
  return line
line1 = line_conf(1, 1)
line2 = line_conf(4, 5)
print(line1(5), line2(5))
          

我们在C程序中适度地模拟其中的line_conf函数:

            
/* MIT License
Copyright (c) 2017 Yuandong-Chen
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE. */
///////////////////////////////////////////////////////////////////////////////
// Note: The C program is almost equivalent to the Python program as follows:
// def line_conf(a, b):
//   def line(x):
//     return a*x + b
//   return line
//
// line1 = line_conf(1, 1)
// line2 = line_conf(4, 5)
// print(line1(5), line2(5))
#include 
            
               
#include 
              
                 
#include 
                
                   
#include 
                  
                    
typedef int Func();
Func *line_conf(int x, int y,...)
{ 
  va_list ap; 
  va_start(ap, y);
  asm volatile(
    "push %%eax\n\t"
    "subl $40, %%esp\n\t"
    "movl 8(%%ebp), %%eax\n\t"
    "movl %%eax, -36(%%ebp)\n\t"
    "movl 12(%%ebp), %%eax\n\t"
    "movl %%eax, -40(%%ebp)\n\t"
    "addl $40, %%esp\n\t"
    "pop %%eax\n\t"
    :::"memory"
    );
if(va_arg(ap,int) == 1){
LINE:
  asm volatile(
    "push %%ebp\n\t"
    "movl %%esp, %%ebp\n\t"
    "movl 8(%%ebp), %%eax\n\t"
    "imul -36(%%ebp), %%eax\n\t"
    "addl -40(%%ebp), %%eax\n\t"
    "movl %%ebp, %%esp\n\t"
    "pop %%ebp\n\t"
    "ret\n\t"
    :::"memory","%eax"
    );
}  
__END: 
  va_end(ap);
  return (Func *)(&&LINE);
}
int main(int argc, const char *argv[]){ 
  printf("====TEST START====\n");
  printf("34*234+6 ?= %d\n",line_conf(34,6)(234));
  printf("1*3+2 ?= %d; 324*65+3 ?= %d; 13*66+2 ?= %d\n",line_conf(1,2)(3),line_conf(324,3)(65),line_conf(13,2)(66));
  int fd = line_conf(1,6)(4);
  Func *fun = line_conf(3,3);
  int a = 1; // Limited point
  printf("3*3+3 ?= %d; 1*4+6 ?= %d\n",fun(3),fd);
  printf("====TEST END====\n");
  return 0; 
}
// Compile it by the following command:
// gcc -m32 -O0 -fno-stack-protector CFunctional.c; ./a.out
// The terminal output should looks like:
// ====TEST START====
// 34*234+6 ?= 7962
// 1*3+2 ?= 5; 324*65+3 ?= 21063; 13*66+2 ?= 860
// 3*3+3 ?= 12; 1*4+6 ?= 10
// ====TEST END====
//Note: The limitation happens between line 86 and line 88, we cannot insert any function here
// whose stack is larger than 40 bytes.(Why is 40? check the inline assembler language)
                  
                
              
            
          

结果在MacOSX和Ubuntu上(i386)都能通过简单的测试。但是可以看到,仅仅是简单的模拟,我们也得用到大量(按比例)的汇编,可读性很差,而且模拟程度非常有限,代码长度也更长。相反,对于这类一般功能的函数,Python可以很容易地模拟C语言的函数,而且模拟程度很高。

以上所述是小编给大家介绍的用C语言模仿Python函数的一种简单实现方法,希望对大家有所帮助,如果大家有任何疑问欢迎给我留言。


更多文章、技术交流、商务合作、联系博主

微信扫码或搜索:z360901061

微信扫一扫加我为好友

QQ号联系: 360901061

您的支持是博主写作最大的动力,如果您喜欢我的文章,感觉我的文章对您有帮助,请用微信扫描下面二维码支持博主2元、5元、10元、20元等您想捐的金额吧,狠狠点击下面给点支持吧,站长非常感激您!手机微信长按不能支付解决办法:请将微信支付二维码保存到相册,切换到微信,然后点击微信右上角扫一扫功能,选择支付二维码完成支付。

【本文对您有帮助就好】

您的支持是博主写作最大的动力,如果您喜欢我的文章,感觉我的文章对您有帮助,请用微信扫描上面二维码支持博主2元、5元、10元、自定义金额等您想捐的金额吧,站长会非常 感谢您的哦!!!

发表我的评论
最新评论 总共0条评论