Question

考虑遵循c代码：

int main (int argc, char *argv[]) {
  MYSQL *sql_handle;

  fprintf(stdout,"initializing handle..\n");
  sql_handle = mysql_init(sql_handle);

  fprintf(stdout,"connecting to database..\n");
  mysql_real_connect(sql_handle,NULL,NULL,
                      NULL,"test",0,NULL,0);

  fprintf(stdout,"connection established\n");
  mysql_close(sql_handle);
}

这会产生以下输出

...
initializing handle..
connecting to database..
initializing handle..
connecting to database..
initializing handle..
connecting to database..
initializing handle..
connecting to database..
connection established
Error: Can't create UNIX socket (24)

real_connect函数似乎有问题。守护进程肯定在运行。很久以前，因为我习惯了，所以这可能是一个愚蠢的问题。

[更新] 这是完整的代码

  1 #include <stdio.h>
  2 #include <stdlib.h>
  3 
  4 #if defined __WIN32__ || _MSC_VER
  5    #include "my_global.h"
  6    #include "mysql.h"
  7 #else
  8    #include <mysql.h>
  9 #endif
 10 
 11 /* prototypes */
 12 void connect(void);
 13 
 14 /* sql handle */
 15 MYSQL *sql_handle;
 16 
 17 int main (int argc, char *argv[]) {
 18   fprintf(stdout,"main..\n");
 19   connect();
 20   return EXIT_SUCCESS;
 21   
 22 } 
 23 void connect(void){
 24   fprintf(stdout,"initializing database handle..\n");
 25   sql_handle = mysql_init(NULL);
 26   
 27   fprintf(stdout,"connecting to database..\n");
 28   mysql_real_connect(sql_handle,NULL,NULL,NULL,NULL,0,NULL,0);
 29   
 30   fprintf(stdout,"closing connection..\n");
 31   mysql_close(sql_handle);
 32 }

此代码生成该输出：

...
connecting to database..
initializing database handle..
connecting to database..
initializing database handle..
connecting to database..
closing connection..
[1]    12914 segmentation fault (core dumped)  ./db

将connect-function的主体复制到main并删除connect-functions解决了这个问题。但这不是解决方案。

Answer 1

重命名方法

void connect(void)

到

void connect_to_database(void)

为我解决了这个问题

Answer 2

我认为问题出在函数connect（）中，它与socket的connect（）名称相同：

int connect（int sockfd，const struct sockaddr * addr，socklen_t addrlen）;

链接时，函数mysql_real_connect（）需要调用connect（）来连接底层套接字，但是调用重新定义的connect（）函数，因此生成了循环。

这就是为什么将connect（）的名称更改为connect_to_database（）解决了这个问题。

Answer 3

我认为你需要一个真正的sql句柄对象

int main (int argc, char *argv[]) {
  MYSQL *sql_handle;

  /* create object */
  sql_handle = malloc(sizeof *sql_handle);

  /* ... */

  /* release object */
  free(sql_handle);
}

或

int main (int argc, char *argv[]) {
  MYSQL sql_handle;        /* create object, not pointer */

  fprintf(stdout,"initializing handle..\n");
  mysql_init(&sql_handle); /* use address */

  fprintf(stdout,"connecting to database..\n");
  mysql_real_connect(&sql_handle,NULL,NULL, /* use address */
                      NULL,"test",0,NULL,0);

  fprintf(stdout,"connection established\n");
  mysql_close(&sql_handle); /* use address */

}

循环mysql_real_connect或什么

3 个答案: