MySQL學習筆記_13_Linux下C++/C串連MySQL資料庫(三)

Linux下C++/C串連MySQL資料庫(三)--處理返回資料

一、通過返回結果集中的欄位數

unsigned int mysql_field_count(MYSQL * connection);//將MYSQL_ROW的值作為一個儲存了一行資料的數組...

樣本：

//一次取一個值的情況，另一種情況與其類似，修改處會標出#include <iostream>#include <fstream>#include <cstdlib>#include <mysql/mysql.h>using namespace std;void mysql_err_function(MYSQL * connection);void mysql_display(MYSQL * mysql,MYSQL_ROW sqlrow);int main(){    MYSQL * connection;    connection = mysql_init(NULL);    if (mysql_real_connect(connection,"localhost","root","123456","test",0,NULL,0))    {        cout << "Connection to MySQL Server is Succeed..." << endl;        string query = "select * from tmp15";        //getline(cin,query);        int res = mysql_query(connection,query.c_str());        if (res)        {            mysql_err_function(connection);        }        else        {            MYSQL_RES * my_res = mysql_use_result(connection);//將mysql_use_result改為mysql_store_result即可得到另一種情況的結果（其實是相同的...）            if (my_res)            {                MYSQL_ROW sqlrow;                while ((sqlrow = mysql_fetch_row(my_res)))                {                    mysql_display(connection,sqlrow);                }                mysql_free_result(my_res);            }            else            {                mysql_err_function(connection);            }        }        mysql_close(connection);        cout << "Connection to MySQL Server is Closed!" << endl;    }    else    {        mysql_err_function(connection);    }}void mysql_err_function(MYSQL * connection){    if (mysql_errno(connection))    {        cout << "Error " << mysql_errno(connection) << " : "             << mysql_error(connection) << endl;        exit(-1);    }}void mysql_display(MYSQL * mysql,MYSQL_ROW sqlrow){    for (unsigned int i = 0; i < mysql_field_count(mysql); ++i)    {        printf("%s ",sqlrow[i]);        //cout << sqlrow[i] << ' ';//不知到為什麼將printf換成cout之後，列印值就會出錯...思考ing...    }    cout << endl;}

二、擷取一個欄位的資訊

1、MYSQL_FIELD *mysql_fetch_field(MYSQL_RES *result);  2、MYSQL_FIELD定義：typedef struct st_mysql_field{    char *name;                        /* Name of column */    char *table;                        /* Table of column if column was a field */    char *org_table;                /* Org table name if table was an alias */    char *db;                        /* Database for table */    char *def;                        /* Default value (set by mysql_list_fields) */    unsigned long length;                /* Width of column */    unsigned long max_length;        /* Max width of selected set */    unsigned int flags;                /* Div flags */    unsigned int decimals;        /* Number of decimals in field */    enum enum_field_types type;        /* Type of field. Se mysql_com.h for types */} MYSQL_FIELD;3、IS_NUM宏，若欄位類型是數字形式的，則返回真。if (IS_NUM(mysql_field_ptr -> type)){cout << "Number" << endl;}4、MYSQL_FIELD_OFFSET mysql_field_seek(MYSQL_RES * result,MYSQL_FIELD_OFFSET offset);//函數將欄位游標設定到給定的位移量offset,下一次調用mysql_fetch_field將檢索與該位移量關聯的列的欄位定義。如果鑰定位行的開始，則要傳遞一個值為0的offset值。

樣本：

#include <iostream>#include <fstream>#include <cstdlib>#include <mysql/mysql.h>using namespace std;void mysql_err_function(MYSQL * connection);//實現參照上例void mysql_display(MYSQL * mysql,MYSQL_ROW sqlrow);//實現參照上例void mysql_display_head(MYSQL_RES * my_res);int main(){    MYSQL * connection;    connection = mysql_init(NULL);    if (mysql_real_connect(connection,"localhost","root","123456","test",0,NULL,0))    {        cout << "Connection to MySQL Server is Succeed..." << endl;        string query = "select * from tmp15";        //getline(cin,query);        int res = mysql_query(connection,query.c_str());        if (res)        {            mysql_err_function(connection);        }        else        {            MYSQL_RES * my_res = mysql_use_result(connection);            if (my_res)            {                mysql_display_head(my_res);                MYSQL_ROW sqlrow;                cout << "Column Details:" << endl;                while ((sqlrow = mysql_fetch_row(my_res)))                {                    mysql_display(connection,sqlrow);                }                mysql_free_result(my_res);            }            else            {                mysql_err_function(connection);            }        }        mysql_close(connection);        cout << "Connection to MySQL Server is Closed!" << endl;    }    else    {        mysql_err_function(connection);    }}void mysql_display_head(MYSQL_RES * my_res){    MYSQL_FIELD * my_field;    cout << "Column Describe:" << endl;    while ((my_field = mysql_fetch_field(my_res)))    {        cout << "\tName: " << my_field -> name << endl;        cout << "\tType: ";        if (IS_NUM(my_field -> type))        {            cout << "Numeric field";        }        else        {            switch(my_field -> type)            {            case FIELD_TYPE_VAR_STRING:                cout << "Varchar";                break;            case FIELD_TYPE_LONG:                cout << "Long";                break;            default:                cout << "is " << my_field -> type << ",check in mysql.h";                break;            }        }        cout << endl;        cout << "\tMax width: " << my_field -> length << endl;        if (my_field -> flags & AUTO_INCREMENT_FLAG)        {            cout << "\tAUTO_INCREMENT" << endl;        }        cout << endl;    }}