动态分配内存的问题
大牛们帮帮 ， 小弟看到指针的时候，遇到了动态分配内存的 问题， pbuffer = (char*)malloc(BUFFER_LEN);这样的我懂 但是下面用红的标出来的，不明白，为什么要这么做呢？完全可以用 pbuffer = (char*)malloc(BUFFER_LEN);这种方式啊。#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define BUFFER_LEN 5 /* Initial length of input buffer */
#define BUFFER_LEN_INCR 2 /* Increment to buffer length */
#define CAPACITY_INCR 2 /* Increment to capacity for proverbs */
int main(void)
{
char **pProverbs = NULL; /* Pointer to string pointer */
char **temp = NULL; /* Temporary pointer to string pointer */
int capacity = 0; /* Number of proverbs that can be stored */
int count = 0; /* Number of proverbs read */
char *pbuffer = NULL; /* Pointer to buffer */
char *pstart = NULL; /* Pointer to buffer start */
char *pstr = NULL; /* Pointer to a string */
int buffer_length = BUFFER_LEN; /* Buffer length */
pbuffer = (char*)malloc(BUFFER_LEN); /* Initial buffer size 这个明白*/
pstart = pbuffer; /* Store start of buffer */
for(;;)
{
if(count==capacity)
{
capacity += CAPACITY_INCR;
temp = (char**)malloc(capacity*sizeof(char*));///这句话不明白
if(!temp) /* If memory was not allocated */
{ /* Output a message and end */
printf("Memory allocation failed. Terminating program.");
exit(1);
}
if(!pProverbs) /* Are there any proverbs? */
pProverbs = temp; /* No - so just copy address of new memory */
else /* Yes - so copy data from old to new */
{
for(int i = 0 ; i<count ; i++)
*(temp+i) = *(pProverbs+i);
free(pProverbs); /* Free the old memory */
pProverbs = temp; /* Copy address of new */
}
temp = NULL; /* Reset pointer */
}
printf("Enter a proverb or press Enter to end:\n");
/* Read a proverb */
while((*pbuffer++ = getchar()) != '\n')
{
if(pbuffer-pstart == buffer_length) /* Check for buffer full */
{
buffer_length += BUFFER_LEN_INCR; /* Increase buffer length */
pstr = (char*)malloc(buffer_length); /* Allocate new buffer */
/* Copy old buffer contents to new */
for(int i = 0; i<pbuffer-pstart ; i++)
*(pstr+i) = *(pstart+i);
pbuffer = pstr+(pbuffer-pstart); /* Address of next position in new */
free(pstart); /* Release old buffer memory */
pstart = pstr; /* Set to start of new buffer */
pstr = NULL; /* Reset pointer */
}
}
/* check for empty line indicating end of input */
if((pbuffer-pstart)<2)
break;
/* Check for string too long */
if((pbuffer - pstart) == BUFFER_LEN && *(pbuffer-1)!= '\n')
{
printf("String too long ?maximum %d characters allowed.",
BUFFER_LEN);
pbuffer = pstart;
continue;
}
*(pbuffer-1) = '\0'; /* Add string terminator */
pbuffer = pstart;
*(pProverbs+count) = (char*)malloc(strlen(pstart)+1);
strcpy(*(pProverbs+count++),pstart);
}
/* Order the proverbs from shortest to longest */
for(int i = 0 ; i<count-1 ; i++)
for(int j = i+1 ; j<count ; j++)
if(strlen(*(pProverbs+i))>strlen(*(pProverbs+j)))
{
pstr = *(pProverbs+i);
*(pProverbs+i) = *(pProverbs+j);
*(pProverbs+j) = pstr;
}
/* Output all the strings */
printf("\nIn ascending length order, the proverbs you entered are:\n");
for (int i = 0 ; i<count ; i++ )
{
printf("\n%s", *(pProverbs + i));
free(*(pProverbs + i)); /* Release the memory for the proverb */
*(pProverbs + i) = NULL; /* Set pointer back to NULL for safety */
}
free(pProverbs); /* Release memory for the pointers */
free(pstart); /* Release memory for the buffer */
}
