通常狀況下,獲取本機 DNS 地址的時候,咱們會使用如下的方法。html
先在系統中加入 libresolv.tbd
庫。 而後在頭文件中引入如下幾個頭文件:服務器
#include <arpa/inet.h>
#include <ifaddrs.h>
#include <resolv.h>
#include <dns.h>
複製代碼
而後使用如下代碼,或者以此進行改編:markdown
NSMutableArray *DNSList = [NSMutableArray array];
res_state res = malloc(sizeof(struct __res_state));
int result = res_ninit(res);
if (result == 0) {
for (int i=0;i < res->nscount;i++) {
NSString *s = [NSString stringWithUTF8String:inet_ntoa(res->nsaddr_list[i].sin_addr)];
[DNSList addObject:s];
}
}
res_nclose(res);
free(res);
// dnsList 就是 DNS 服務器地址
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可是不巧,不就有個朋友告訴我,使用這段代碼會形成內存泄漏,我本身試了一下,還真有,那是哪裏出了問題呢?oracle
通過初步的檢測,發現 int result = res_ninit(res);
這段代碼建立的內存沒有釋放掉。函數
可是下面明明已經寫了 res_nclose(res);
了啊。oop
沒辦法,我點擊進入 res_ninit
的頁面,挨個進行查找。ui
終於在通過了漫長的翻閱資料以後,發現了一份 Oracle 的文檔。this
裏面有幾段註釋讓我如獲至寶:spa
The res_ndestroy() function should be called to free memory allocated by res_ninit() after the last use of statp.code
The res_nclose() function closes any open files referenced through statp.
The res_ndestroy() function calls res_nclose(), then frees any memory allocated by res_ninit() referenced through statp.
以及下面這段示例代碼:
#include <resolv.h>
#include <string.h>
int main(int argc, char **argv) {
int len;
struct __res_state statp;
union msg {
uchar_t buf[NS_MAXMSG];
HEADER h;
} resbuf;
/* Initialize resolver */
memset(&statp, 0, sizeof(statp));
if (res_ninit(&statp) < 0) {
fprintf(stderr, "Can't initialize statp.\n");
return (1);
}
/* * Turning on DEBUG mode keeps this example simple, * without need to output anything. */
statp.options |= RES_DEBUG;
/* Search for A type records */
len = res_nsearch(&statp, "example.com", C_IN, T_A,
resbuf.buf, NS_MAXMSG);
if (len < 0) {
fprintf(stderr, "Error occured during search.\n");
return (1);
}
if (len > NS_MAXMSG) {
fprintf(stderr, "The buffer is too small.\n");
return (1);
}
/* ... Process the received answer ... */
/* Cleanup */
res_ndestroy(&statp);
return (0);
}
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意思就是:
NSMutableArray *DNSList = [NSMutableArray array];
res_state res = malloc(sizeof(struct __res_state));
int result = res_ninit(res);
if (result == 0) {
for (int i=0;i < res->nscount;i++) {
NSString *s = [NSString stringWithUTF8String:inet_ntoa(res->nsaddr_list[i].sin_addr)];
[DNSList addObject:s];
}
}
res_ndestroy(res);
free(res);
// dnsList 就是 DNS 服務器地址
複製代碼