"iOS Dev-104" SQLite uses: Note Query time-of-step write while there is a dead loop

Note the point:

In a select query, you cannot step into the following form, or a dead loop will occur:

int Stepresult=sqlite3_step (statement); while (Stepresult==sqlite_row) {}

Can only be combined into one sentence to write:

while (Sqlite3_step (statement) ==sqlite_row) {         }

Because, the sqlite3_step is executed as follows:

* * ^if The SQL statement being executed returns any data and then [Sqlite_row]

* * is returned each time a new row of data are ready for processing by the

* * caller. The values may accessed using the [column access functions].

* * SQLITE3_STEP () is called again to retrieve the next row of data.

#import "ViewController.h" #import <sqlite3.h> @interface Viewcontroller ()-(ibaction) Insert: (ID) sender;-( ibaction) Delete: (ID) sender;-(ibaction) Update: (ID) sender;-(ibaction) Select: (ID) sender; @end @implementation    Viewcontrollerstatic sqlite3 *_db;-(void) viewdidload {[Self setupdatabaseandtable];    [Super Viewdidload]; Do any additional setup after loading the view, typically from a nib.}    -(void) didreceivememorywarning {[Super didreceivememorywarning]; Dispose of any resources the can be recreated.} -(void) setupdatabaseandtable{nsstring *filename=[[nssearchpathfordirectoriesindomains (NSDocumentDirectory,    Nsuserdomainmask, YES) lastobject] stringbyappendingpathcomponent:@ "Ios.sql"];        NSLog (@ "%@", filename); int Opendbresult=sqlite3_open (filename.        Utf8string, &_db); if (OPENDBRESULT==SQLITE_OK) {//CREATE TABLE NSString *[email protected] "CREATE TABLE IF not EXISTS user (ID in Teger PRIMARY KEY autoincrement,name text,age INTEGER);";        Char *error=nil;        int Createtableresult=sqlite3_exec (_db, createtablesql.utf8string, NULL, 0, &error);        if (CREATETABLERESULT==SQLITE_OK) {NSLog (@ "CREATE table succeeded");        }else{NSLog (@ "CREATE TABLE failed");    } NSLog (@ "Open database succeeded");    }else{NSLog (@ "Failed to open database"); }}-(ibaction) Insert: (ID) sender {for (int i=0; i<50; i++) {nsstring *name=[nsstring stringwithformat:@ "Jack        %d ", Arc4random ()%100];        int age=arc4random ()%100;        NSString *inserttablesql=[nsstring stringwithformat:@ "INSERT into User (name,age) VALUES ('%@ ',%d);", Name,age];        Char *error=nil;        int Insertresult=sqlite3_exec (_db, inserttablesql.utf8string, NULL, 0, &error);        if (INSERTRESULT==SQLITE_OK) {NSLog (@ "%d%@%d", i,name,age);        }else{NSLog (@ "Insert data failed");    }}}-(Ibaction) Delete: (ID) Sender {nsstring *[email protected] "Delete from user WHERE id=1;";    Char *error=nil; int Deleteresult=sqlIte3_exec (_db, deleterowsql.utf8string, NULL, 0, &error);    if (DELETERESULT==SQLITE_OK) {NSLog (@ "Delete data succeeded");    }else{NSLog (@ "Delete data failed");    }}-(ibaction) Update: (ID) Sender {nsstring *[email protected] "Update user SET age=130 WHERE id=3;";    Char *error=nil;    int Updateresult=sqlite3_exec (_db, updaterowsql.utf8string, NULL, 0, &error);    if (UPDATERESULT==SQLITE_OK) {NSLog (@ "Modify database Success");    }else{NSLog (@ "Failed to modify database");    }}-(ibaction) Select: (ID) Sender {nsstring *[email protected] "Select id,name,age from User WHERE id=5;";    Sqlite3_stmt *statement;    int Stmtresult=sqlite3_prepare_v2 (_db, Selectrowsql.utf8string,-1, &statement, nil);        if (STMTRESULT==SQLITE_OK) {NSLog (@ "stmtresult success");            The following statement will appear in a dead loop while (Sqlite3_step (statement) ==sqlite_row) {NSLog (@ "Stepresult succeeded");            int Uid=sqlite3_column_int (statement, 0); Const unsigned char *uname=sqlite3_column_text (statement, 1);            int Uage=sqlite3_column_int (statement, 2);        NSLog (@ "%d%s%d", uid,uname,uage);    }}else{NSLog (@ "Stmtresult failed"); }} @end

"iOS Dev-104" SQLite uses: Note Query time-of-step write while there is a dead loop