MySQL study note _ C ++/C in 13_Linux connect to MySQL database (3) -- Process returned data

Connect C ++/C to MySQL database in Linux (3) -- Process returned data 1. Number of fields in the returned result set

Unsigned int mysql_field_count (MYSQL * connection); // use the value of MYSQL_ROW as an array that stores a row of data...

Example:

// When one value is obtained at a time, the other is similar, # 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 Serve R 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 ); // change mysql_use_result to mysql_store_result to get the result of another situation (actually the same ...) if (my_res) {MYSQL_ROW sqlrow; while (sqlrow = mysql_fetch_row (my_res) {mysql_display (connectio N, 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] <''; // if you change printf to cout, an error occurs when you print the value... think about ing ...} cout <endl ;}

2. obtain the information of a field

1. MYSQL_FIELD * mysql_fetch_field (MYSQL_RES * result); 2. MYSQL_FIELD definition: 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 macro. If the field type is numeric, true is returned. If (IS_NUM (mysql_field_ptr-> type) {cout <"Number" <endl;} 4. MYSQL_FIELD_OFFSET mysql_field_seek (MYSQL_RES * result, MYSQL_FIELD_OFFSET offset ); // The function sets the field cursor to the given offset. The next call of mysql_fetch_field will retrieve the field definitions of the columns associated with the offset. If the key locates the beginning of the row, an offset value with a value of 0 will be passed.

Example:

# Include <iostream> # include <fstream> # include <cstdlib> # include <mysql/mysql. h> using namespace std; void mysql_err_function (MYSQL * connection); // the preceding example shows void mysql_display (MYSQL * mysql, MYSQL_ROW sqlrow ); // for implementation, see the preceding example 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) {co Ut <"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 ;}}