getline()函數

    我在網上搜了半天getline()函數，大多針對C++的，重載函數比較多，雲裡霧裡的，而且沒有執行個體，反正就是沒有自己所需要的getline()函數。是以，自己在Linux下man了一把，并做了測試。getline()函數的功能是從檔案中擷取行資訊，即每次讀取一行資訊。

    因為我使用getline()函數的目的是擷取本地網卡資訊，即eth0的資訊，進而判斷啟動機子時是否查了網線（本來可以從驅動裡做，但應用層可以搞定，就不想多做處理了，諒解）。

//函數原型

#define _GNU_SOURCE

#include <stdio.h>

      ssize_t getline(char **lineptr, size_t *n, FILE *stream);

       ssize_t getdelim(char **lineptr, size_t *n, int delim, FILE*stream);

[[email protected] for_test]# cat dev

Inter-|   Receive                                                | Transmit

 face |bytes   packets errs drop fifo frame compressed multicast|bytes    packets errs drop fifo colls carriercompressed

   lo:       0       0   0    0    0    0          0         0        0      0    0    0   0     0       0         0

 eth0:  53311     230    0    0   0     0          0        0     5370      33   0    0    0    0       0          0

[[email protected] for_test]# cat eth0_dev.c

#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)))//讀取行資訊，'\n'為換行标志
    {
        pstr = strstr(line, "eth0");//查找改行中是否有"eth0"的字元串
        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;
        }
    }
    //確定空間的釋放
    if(line)
    {
        free(line);
    }
    fclose(fp);
	return 0;
}
           

[[email protected] for_test]#gcc eth0_dev.c

[[email protected] for_test]# ./a.out

buf1:eth0:  buf2:53311 buf3:230

[[email protected] for_test]# man getline

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.