C编程的本地字符指针

Question

我有一个函数，它返回前n个字符，直到到达指定的字符。我想传递一个ptr，将其设置为字符串中的下一个单词；我该如何做到这一点？这是我当前的代码。

char* extract_word(char* ptrToNext, char* line, char parseChar)
// gets a substring from line till a space is found
// POST: word is returned as the first n characters read until parseChar occurs in line
//      FCTVAL == a ptr to the next word in line
{
   int i = 0;
   while(line[i] != parseChar && line[i] != '' && line[i] != 'n')
   {
      i++;
   }
   printf("line + i + 1: %cn", *(line + i + 1));  //testing and debugging
   ptrToNext = (line + i + 1);    // HELP ME WITH THIS! I know when the function returns
                                  //   ptrToNext will have a garbage value because local
                                  //   variables are declared on the stack
   char* temp = malloc(i + 1);
   for(int j = 0; j < i; j++)
   {
      temp[j] = line[j];
   }
   temp[i+1] = '';
   char* word = strdup(temp);
   return word;
}

Answer 1

您可以传递一个参数，该参数是指向char的指针；然后在函数中，您可以更改指向指针的值。换句话说，

char * line = ...;
char * next;
char * word = extract_word(&next, line, 'q');

在你的职能范围内。。。

// Note that "*" -- we're dereferencing ptrToNext so
// we set the value of the pointed-to pointer.
*ptrToNext = (line + i + 1);

Answer 2

有一些库函数可以帮助您解决strspn（）strcspn（）这类问题。

#include <stdlib.h>
#include <string.h>
char *getword(char *src, char parsechar)
{
char *result;
size_t len;
char needle[3] = "nn" ;
needle[1] = parsechar;
len = strcspn(src, needle);
result = malloc (1+len);
if (! result) return NULL;
memcpy(result, str, len);
result[len] = 0;
return result;
}