我在網上搜了半天getline()函數，大多針對C++的，重載函數比較多，云里霧里的，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，并做了測試。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（本來可以從驅動里做，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
?
#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
?
?
?
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.
以上就是本文關于C語言中getline()函數的深入理解，希望對大家有所幫助，如有不足之處，請留言，小編會及時更正。感謝朋友們對武林技術頻道的支持！
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