C令牌化多项式系数 [英] C tokenize polynomial coefficients

问题描述

我试图将来自char数组的多项式的系数放到一个int数组中

我有这个：

char string [] =-4x ^ 0 + x ^ 1 + 4x ^ 3 - 3x ^ 4;

可以用空格将其标记为

-4x ^ 0

x ^ 1

4x ^ 3

3x ^ 4

所以我试图得到：-4，1,4,3成一个int数组

  int * coefficient; 
 coefficient = new int [counter]; 
 
 p = strtok（copy，+）; 
 int a; 
 while（p）
 {
 int z = 0; 
 while（p [z]！='x'）
 z ++; 
 char temp [z]; 
 strncpy（temp [z]，p，z）; 
 coefficient [a] = atoi（temp）; 
 p = strtok（NULL，+）; 
 a ++; 
} 
  

但是，我得到一个错误，我无法转换char *
on strncpy（temp [z]，p，z）;

 错误： 'char *'
错误：初始化'char * strncpy（char *，const char *，size_t）'的参数1 
  

$ b b

这是最好的方法是什么？

解决方案

b
$ b

  strncpy（temp [z]，p，z）; 
  

需要：

  strncpy（temp，p，z）; 
  

但请记住， strncpy null-terminate the string。

此外， z 将是系数的长度，

更新：

检查您的链接，我仍然看到几个严重问题：

• 您不能在 strtok 中使用 - 拿起-4x中的一个以及你想要的。


• strncpy 函数将字符串un-终止，这可能导致 atoi 崩溃或随机给出错误的值。一种习惯的形式是手动编写终止符，例如 temp [z] ='\0'。


• 没有得到任何输出值是系数[a] = 正在写入一些随机存储器，因为 a 未初始化。

I'm trying to put the coefficients of polynomials from a char array into an int array
I have this:

char string[] = "-4x^0 + x^1 + 4x^3 - 3x^4";

and can tokenize it by the space into
-4x^0
x^1
4x^3
3x^4

So I am trying to get: -4, 1, 4, 3 into an int array

 int *coefficient;
 coefficient = new int[counter];

 p = strtok(copy, "  +");
 int a;
 while (p)
 {
  int z = 0;
  while (p[z] != 'x')
   z++;
  char temp[z];
  strncpy(temp[z], p, z);
  coefficient[a] = atoi(temp);
  p = strtok(NULL, "  +");
  a++;
 }

However, Im getting an error that I cant convert a char* into a char on strncpy(temp[z], p, z);

error: invalid conversion from ‘char’ to ‘char*’  
error: initializing argument 1 of ‘char* strncpy(char*, const char*, size_t)’

What would be the best way to do this?

解决方案

This:

strncpy(temp[z], p, z);

Needs to be:

strncpy(temp, p, z);

But remember that strncpy doesn't always null-terminate the string.

Also, z will be the length of the coefficient, but you need an extra byte in the buffer for the null terminator.

Update:

examining your link, I still see several serious problems:

• You can't use "-" in strtok because it will pick up the one in "-4x" as well as the ones you want. I think you should split on spaces only and handle the +/- operators as tokens.
• The strncpy function leaves the string un-terminated, which may cause atoi to crash or give the wrong value randomly. One idiomatic form is to write the terminator manually, e.g., temp[z] = '\0'.
• The reason you're not getting any output values is that coefficient[a] = is writing to some random memory because a is uninitialized.

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