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mysql C语言API接口及实例

發布時間：2025/5/22 数据库 16 豆豆

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Mysql數據庫動態庫：?libmysql.dll??libmysql.lib?mysql.h??WinSock2.h

Mysql?API數據結構???(mysql.h)

???????MYSQL:連接數據庫前，必須先創建MYSQL變量，此變量在很多Mysql?API函數會用到。它包含了一些連接信息等數據。

???????MYSQL_RES:MYSQL_RES結構體中包含了查詢結果集，也就是從數據庫中查詢到的數據。可以使用mysql_store_result或mysql_use_result函數獲得。

???????MYSQL_ROW:MYSQL?ROW的定義如下：typedef?char?**MYSQL_ROW;可見，它實際上是char?**類型，指向一個字符串數組。存儲一行中各段字符數組，可以通過mysql_fetch_row函數獲得。

???????MYSQL_FIELD:MYSQL_FIELD中包含了字段名、字段類型和大小等信息。可以重復調用mysql_fetch_field函數獲得所有字段的信息。

?????Mysql?C?API編程步驟

1、首先我們要包含mysql的頭文件，并鏈接mysql動態庫。

#include?<WinSock2.h>??????//?進行網絡編程需要winsock2.h???

#include?<mysql.h>???

#pragma?comment(lib,?"libmysql.lib")??

?2、創建MYSQL變量。如：

???????MYSQL?mysql;

3、初始化MYSQL變量。

???????mysql_init(&mysql);

?4、調用mysql_real_connect函數連接Mysql數據庫。

mysql_real_connect函數的MYSQL?*??STDCALL?mysql_real_connect(MYSQL?*mysql,?const?char?*host,const?char?*user,const?char?*passwd,const?char?*db,unsigned?int?port,const?char?*unix_socket,unsigned?long?clientflag);????

???????參數說明：mysql--前面定義的MYSQL變量；host--MYSQL服務器的地址；user--登錄用戶名；passwd--登錄密碼；db--要連接的數據庫；port--MYSQL服務器的TCP服務端口；unix_socket--unix連接方式，為NULL時表示不使用socket或管道機制；clientflag--Mysql運行為ODBC數據庫的標記，一般取0。

???????連接失敗時該函數返回0。

?5、調用mysql_real_query函數進行數據庫查詢。mysql_real_query函數的原型如下：

???????int??STDCALL?mysql_real_query(MYSQL?*mysql,?const?char?*q,?unsigned?long?length);

???????參數說明：mysql--前面定義的MYSQL變量；q--SQL查詢語句；length--查詢語句的長度。

???????查詢成功則該函數返回0。

???????6、通過調用mysql_store_result或mysql_use_result函數返回的MYSQL_RES變量獲取查詢結果數據。

???????兩個函數的原型分別為：

???????MYSQL_RES?*?????STDCALL?mysql_store_result(MYSQL?*mysql);

???????MYSQL_RES?*?????STDCALL?mysql_use_result(MYSQL?*mysql);

???????這兩個函數分別代表了獲取查詢結果的兩種方式。第一種，調用mysql_store_result函數將從Mysql服務器查詢的所有數據都存儲到客戶端，然后讀取；第二種，調用mysql_use_result初始化檢索，以便于后面一行一行的讀取結果集，而它本身并沒有從服務器讀取任何數據，這種方式較之第一種速度更快且所需內存更少，但它會綁定服務器，阻止其他線程更新任何表，而且必須重復執行mysql_fetch_row讀取數據，直至返回NULL，否則未讀取的行會在下一次查詢時作為結果的一部分返回，故經常我們使用mysql_store_result。

???????7、調用mysql_fetch_row函數讀取結果集數據。

???????上述兩種方式最后都是重復調用mysql_fetch_row函數讀取數據。mysql_fetch_row函數的原型如下：

???????MYSQL_ROW?STDCALL?mysql_fetch_row(MYSQL_RES?*result);

???????參數result就是mysql_store_result或mysql_use_result的返回值。

???????該函數返回MYSQL_ROW型的變量，即字符串數組，假設為row，則row[i]為第i個字段的值。當到結果集尾部時，此函數返回NULL。

???????8、結果集用完后，調用mysql_free_result函數釋放結果集，以防內存泄露。mysql_free_result函數的原型如下：

???????void??STDCALL?mysql_free_result(MYSQL_RES?*result);

???????9、不再查詢Mysql數據庫時，調用mysql_close函數關閉數據庫連接。mysql_close函數的原型為：

???????void?STDCALL?mysql_close(MYSQL?*sock);

例子：

1.?int?main()??{?

2.?????MYSQL?mysql;??

3.?????MYSQL_RES?*res;??

4.?????MYSQL_ROW?row;??

5.?????mysql_init(&mysql);??//?初始化MYSQL變量??

6.?????//?連接Mysql服務器，本例使用本機作為服務器。訪問的數據庫名稱為"msyql"，參數中的user為你的登錄用戶名，***為登錄密碼，需要根據你的實際用戶進行設置??

7.?????if?(!mysql_real_connect(&mysql,?"127.0.0.1",?"user",?"123",?"mysql",?3306,?0,?0))??{??

8.?????????cout?<<?"mysql_real_connect?failure!"?<<?endl;??

9.?????????return?0;??

10.?????}??

11.?????if?(mysql_real_query(&mysql,?"select?*?from?user",?(unsigned?long)strlen("select?*?from?user"))){????//?查詢mysql數據庫中的user表?

12.?????????cout?<<?"mysql_real_query?failure!"?<<?endl;??

13.?????????return?0;??

14.?????}??//?存儲結果集??

15.?????res?=?mysql_store_result(&mysql);??

16.?????if?(NULL?==?res)?{??

17.?????????cout?<<?"mysql_store_result?failure!"?<<?endl;??

18.?????????return?0;??

19.?????}??

20.?????//?重復讀取行，并輸出第一個字段的值，直到row為NULL??

21.?????while?(row?=?mysql_fetch_row(res))??{??

22.?????????cout?<<?row[0]?<<?endl;??

23.?????}??

24.?????mysql_free_result(res);??//?釋放結果集???

25.?????mysql_close(&mysql);??//?關閉Mysql連接

26.???????return?0;??}??

10.Char?*?mysql_get_client_info()?顯示mysql客戶端版本

??MySQL?client?version:?5.0.38

11.int?mysql_num_fields(MYSQL_RES?*result)?返回結果子表中域(字段)的個數

12.?MYSQL_FIELD?*?mysql_fetch_field(MYSQL_RES?*result)?返回結果子表中的域結構體指針

13.Void?mysql_real_escape_string(MYSQL*?con,?char*?savedata,?char?*data,?int?size)?在將二進制數據(非文本)保存到數據庫之前，需要轉義，否則數據庫不能正常保存，取出數據時，無需解轉移。轉義時一個字符轉義后2個字符，所以savedata內存必須為data的2倍

14.?unsigned?long?*?mysql_fetch_lengths(MYSQL_RES?*result)?獲取結果中各個字符串的長度，返回為1維數組

一些有用的例子：

#include?

int?main(int?argc,?char?**argv)

{

??MYSQL?*conn;

??MYSQL_RES?*result;

??MYSQL_ROW?row;

??int?num_fields;

??int?i;

??conn?=?mysql_init(NULL);

??mysql_real_connect(conn,?"localhost",?"zetcode",?"passwd",?"testdb",?0,?NULL,?0);

??mysql_query(conn,?"SELECT?*?FROM?writers");

??result?=?mysql_store_result(conn);

??num_fields?=?mysql_num_fields(result);

??while?((row?=?mysql_fetch_row(result)))

??{

??????for(i?=?0;?i?<?num_fields;?i++)

??????{

??????????printf("%s?",?row[i]???row[i]?:?"NULL");

??????}

??????printf("\n");

??}

??mysql_free_result(result);

??mysql_close(conn);

}

The?example?prints?all?names?from?the?writers?table.

$?./select

Leo?Tolstoy

Jack?London

Honore?de?Balzac

Lion?Feuchtwanger

Emile?Zola

?mysql_query(conn,?"SELECT?*?FROM?writers");

We?execute?the?query,?that?will?retrieve?all?names?from?the?writers?database.

?result?=?mysql_store_result(conn);

We?get?the?result?set.

?num_fields?=?mysql_num_fields(result);

We?get?the?number?of?fields?in?the?table.

?while?((row?=?mysql_fetch_row(result)))

?????for(i?=?0;?i?<?num_fields;?i++)

?????{

?????????printf("%s?",?row[i]???row[i]?:?"NULL");

?????}

?????printf("\n");

We?fetch?the?rows?and?print?them?to?the?screen.

?mysql_free_result(result);

We?free?the?resources.

Column?headers

In?the?next?example,?we?will?retrieve?data?and?show?the?their?column?names?from?the?table.

For?this,?we?will?create?a?new?table?friends.

?mysql>?create?table?friends?(id?int?not?null?primary?key?auto_increment,

???????????????????????????????name?varchar(20),?age?int);

?mysql>?insert?into?friends(name,?age)?values('Tom',?25);

?mysql>?insert?into?friends(name,?age)?values('Elisabeth',?32);

?mysql>?insert?into?friends(name,?age)?values('Jane',?22);

?mysql>?insert?into?friends(name,?age)?values('Luke',?28);

We?insert?some?data?into?the?table.

#include?

int?main(int?argc,?char?**argv)

{

??MYSQL?*conn;

??MYSQL_RES?*result;

??MYSQL_ROW?row;

??MYSQL_FIELD?*field;

??int?num_fields;

??int?i;

??conn?=?mysql_init(NULL);

??mysql_real_connect(conn,?"localhost",?"zetcode",?"passwd",?"testdb",?0,?NULL,?0);

??mysql_query(conn,?"SELECT?*?FROM?friends");

??result?=?mysql_store_result(conn);

??num_fields?=?mysql_num_fields(result);

??while?((row?=?mysql_fetch_row(result)))

??{

??????for(i?=?0;?i?<?num_fields;?i++)

??????{

??????????if?(i?==?0)?{

?????????????while(field?=?mysql_fetch_field(result))?{

????????????????printf("%s?",?field->name);

?????????????}

??????????printf("\n");

??????????}

??????????printf("%s??",?row[i]???row[i]?:?"NULL");

??????}

??}

??printf("\n");

??mysql_free_result(result);

??mysql_close(conn);

}

The?example?is?similar?to?the?previous?one.?It?just?adds?column?header?names?to?it.

?while(field?=?mysql_fetch_field(result))?{

?????printf("%s?",?field->name);

The?mysql_fetch_field()?call?returns?a?MYSQL_FIELD?structure.?We?get?the?column?header?names?from?this?structure.

$?./headers

id?name?age

1??Tom??25

2??Elisabeth??32

3??Jane??22

4??Luke??28

And?this?is?the?output?of?our?program.

Inserting?p_w_picpaths?into?MySQL?database

Some?people?prefer?to?put?their?p_w_picpaths?into?the?database,?some?prefer?to?keep?them?on?the?file?system?for?their?applications.?Technical?difficulties?arise?when?we?work?with?millions?of?p_w_picpaths.?Images?are?binary?data.?MySQL?database?has?a?special?data?type?to?store?binary?data?called?BLOB?(Binary?Large?Object).

mysql>?describe?p_w_picpaths;

+-------+------------+------+-----+---------+-------+

+-------+------------+------+-----+---------+-------+

|?id????|?int(11)????|?NO???|?PRI?|?????????|???????|

|?data??|?mediumblob?|?YES??|?????|?NULL????|???????|

+-------+------------+------+-----+---------+-------+

2?rows?in?set?(0.00?sec)

This?is?the?table,?that?we?will?use?in?our?example.?It?can?be?created?by?the?following?SQL?statement.

create?table?p_w_picpaths(id?int?not?null?primary?key,?data?mediumblob);

#include?

int?main(int?argc,?char?**argv)

{

??MYSQL?*conn;

??int?len,?size;

??char?data[1000*1024];

??char?chunk[2*1000*1024+1];

??char?query[1024*5000];

??FILE?*fp;

??conn?=?mysql_init(NULL);

??mysql_real_connect(conn,?"localhost",?"zetcode",?"passwd",?"testdb",?0,?NULL,?0);

??fp?=?fopen("p_w_picpath.png",?"rb");

??size?=?fread(data,?1,?1024*1000,?fp);

??mysql_real_escape_string(conn,?chunk,?data,?size);

??char?*stat?=?"INSERT?INTO?p_w_picpaths(id,?data)?VALUES('1',?'%s')";

??len?=?snprintf(query,?sizeof(stat)+sizeof(chunk)?,?stat,?chunk);

??mysql_real_query(conn,?query,?len);

??fclose(fp);

??mysql_close(conn);

}

In?this?example,?we?will?insert?one?p_w_picpath?into?the?p_w_picpaths?table.?The?p_w_picpath?can?be?max?1?MB.

?fp?=?fopen("p_w_picpath.png",?"rb");

?size?=?fread(data,?1,?1024*1000,?fp);

Here?we?open?the?p_w_picpath?and?read?it?into?the?data?array.

?mysql_real_escape_string(conn,?chunk,?data,?size);

Binary?data?can?obtain?special?characters,?that?might?cause?troubles?in?the?statements.?We?must?escape?them.?The?mysql_real_escape_string()?puts?the?encoded?data?into?the?chunk?array.?In?theory,?every?character?might?be?a?special?character.?That's?why?the?chunk?array?two?times?as?big?as?the?data?array.?The?function?also?adds?a?terminating?null?character.

?char?*stat?=?"INSERT?INTO?p_w_picpaths(id,?data)?VALUES('1',?'%s')";

?len?=?snprintf(query,?sizeof(stat)+sizeof(chunk)?,?stat,?chunk);

These?two?code?lines?prepare?the?MySQL?query.

?mysql_real_query(conn,?query,?len);

Finally,?we?execute?the?query.

Selecting?p_w_picpaths?from?MySQL?database

In?the?previous?example,?we?have?inserted?an?p_w_picpath?into?the?database.?In?the?following?example,?we?will?select?the?inserted?p_w_picpath?back?from?the?database.

#include?

int?main(int?argc,?char?**argv)

{

??MYSQL?*conn;

??MYSQL_RES?*result;

??MYSQL_ROW?row;

??unsigned?long?*lengths;

??FILE?*fp;

??conn?=?mysql_init(NULL);

??mysql_real_connect(conn,?"localhost",?"zetcode",?"passwd",?"testdb",?0,?NULL,?0);

??fp?=?fopen("p_w_picpath.png",?"wb");

??mysql_query(conn,?"SELECT?data?FROM?p_w_picpaths?WHERE?id=1");

??result?=?mysql_store_result(conn);

??row?=?mysql_fetch_row(result);

??lengths?=?mysql_fetch_lengths(result);

??fwrite(row[0],?lengths[0],?1,?fp);

??mysql_free_result(result);

??fclose(fp);

??mysql_close(conn);

}

In?this?example,?we?will?create?an?p_w_picpath?file?from?the?database.

?fp?=?fopen("p_w_picpath.png",?"wb");

We?open?a?file?for?writing.

?mysql_query(conn,?"SELECT?data?FROM?p_w_picpaths?WHERE?id=1");

We?select?an?p_w_picpath?with?id?1.

?row?=?mysql_fetch_row(result);

The?row?contains?raw?data.

?lengths?=?mysql_fetch_lengths(result);

We?get?the?length?of?the?p_w_picpath.

?fwrite(row[0],?lengths[0],?1,?fp);

We?create?the?p_w_picpath?file?using?the?fwrite()?standard?function?call.?

轉載于:https://blog.51cto.com/a1liujin/1686202

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