C语言中getline()函数的深入理解

#include <stdio.h>
#include <string.h>
int main(void)
{
 FILE *fp = NULL;
    int cnt = -1;
    int len = 0;
 char buf1[16] = {0}, buf2[16] = {0}, buf3[16] = {0};
    char *line = NULL;
    char *pstr = NULL; 
 fp = fopen("./dev", "rb");
 if(NULL == fp)
 {
  printf("open /proc/net/dev err!\n");
  return -1;
 }
    while(-1 != (cnt = getline(&line, &len, fp)))//读取行信息，'\n'为换行标志
    {
        pstr = strstr(line, "eth0");//查找改行中是否有"eth0"的字符串
        if(NULL != pstr)
        {
   //printf("%s\n", pstr);
   sscanf(pstr, "%s\t%s\t%s", buf1, buf2, buf3);
   printf("buf1:%s  buf2:%s  buf3:%s\n", buf1, buf2, buf3);
   break;
        }
    }
    //确保空间的释放
    if(line)
    {
        free(line);
    }
    fclose(fp);
 return 0;
}

DESCRIPTION
       getline()  reads  an entire line from stream, storing the address of the buffer containing the text into *lineptr.  The buffer is null-
       terminated and includes the newline character, if one was found.
       If *lineptr is NULL, then getline() will allocate a buffer for storing the line, which should be freed by the user  program.   Alterna-
       tively,  before calling getline(), *lineptr can contain a pointer to a malloc()-allocated buffer *n bytes in size. If the buffer is not
       large enough to hold the line, getline() resizes it with realloc(), updating *lineptr and *n as necessary. In either case,  on  a  suc-
       cessful call, *lineptr and *n will be updated to reflect the buffer address and allocated size respectively.
       getdelim()  works  like  getline(), except a line delimiter other than newline can be specified as the delimiter argument. As with get-
       line(), a delimiter character is not added if one was not present in the input before end of file was reached.
RETURN VALUE
       On success, getline() and getdelim() return the number of characters read, including the delimiter character,  but  not  including  the
       terminating null byte. This value can be used to handle embedded null bytes in the line read.
       Both functions return -1  on failure to read a line (including end of file condition).
ERRORS
       EINVAL Bad parameters (n or lineptr is NULL, or stream is not valid).
EXAMPLE
       #define _GNU_SOURCE
       #include <stdio.h>
       #include <stdlib.h>
       int main(void)
       {
            FILE * fp;
            char * line = NULL;
            size_t len = 0;
            ssize_t read;
            fp = fopen("/etc/motd", "r");
            if (fp == NULL)
                 exit(EXIT_FAILURE);
            while ((read = getline(&line, &len, fp)) != -1) {
                 printf("Retrieved line of length %zu :\n", read);
                 printf("%s", line);
            }
            if (line)
                 free(line);
            return EXIT_SUCCESS;
       }
CONFORMING TO
       Both getline() and getdelim() are GNU extensions.  They are available since libc 4.6.27.