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，而且沒有實例，反正就是沒有自己所需要的getline()函數。所以，自己在Linux下man了一把，並做了測試。getline()函數的功能是從文件中獲取行信息，即每次讀取一行信息。
因為我使用getline()函數的目的是獲取本地網卡信息，即eth0的信息，從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);
[root@localhost 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
[root@localhost for_test]# cat eth0_dev.c
代碼如下：
#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)))//讀取行信息，'\n'為換行標志
{
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;
}
}
//確保空間的釋放
if(line)
{
free(line);
}
fclose(fp);
return 0;
}
[root@localhost for_test]#gcc eth0_dev.c
[root@localhost for_test]# ./a.out
buf1:eth0: buf2:53311 buf3:230
[root@localhost for_test]# man getline
代碼如下：
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.
