Detailed explanation of IOS file read and write operations and simple examples

- (IBAction)btnWrite:(id)sender {
  //Create a file manager  NSFileManager *fileManager = [NSFileManager defaultManager];
  //Get the path  //What kind of path to get  NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
  NSString *documentDirectory = [paths objectAtIndex:0];//Remove the required path  //Change to the operation directory  [fileManager changeCurrentDirectoryPath:[documentDirectory stringByExpandingTildeInPath]];
   //Create file fileName file name, contents file content, if there is no content at the beginning, it can be set to nil, attributes file attributes, initially nil  [fileManager createFileAtPath:@"fileName" contents:nil attributes:nil];
  //Delete the file to be deleted  [fileManager removeItemAtPath:@"createNewFile" error:nil];
  //Get file path  NSString *path = [documentDirectory stringByAppendingPathComponent:@"fileName"];
  NSLog(@"path == %@",path);
  //Data to be written  NSString *temp = @"Hello world";
  int data0 = 1000000;
  float data2 = 23.23f;
  //Create data buffering  NSMutableData *writer = [[NSMutableData alloc]init];
  //Add string to buffer  [writer appendData:[temp dataUsingEncoding:NSUTF8StringEncoding]];
  [writer appendBytes:&data0 length:sizeof(data0)];
  [writer appendBytes:&data2 length:sizeof(data2)];
   
  [writer writeToFile:path atomically:YES];
  [writer release];  
}

- (IBAction)btnRead:(id)sender {
  //Create a file manager  NSFileManager *fileManager = [NSFileManager defaultManager];
  //Get the path  //What kind of path to get  NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
  NSString *documentDirectory = [paths objectAtIndex:0];//Remove the required path  //Change to the operation directory  [fileManager changeCurrentDirectoryPath:[documentDirectory stringByExpandingTildeInPath]];
   //Create file fileName file name, contents file content, if there is no content at the beginning, it can be set to nil, attributes file attributes, initially nil  [fileManager createFileAtPath:@"fileName" contents:nil attributes:nil];
  //Delete the file to be deleted  [fileManager removeItemAtPath:@"createNewFile" error:nil];
  //Get file path  NSString *path = [documentDirectory stringByAppendingPathComponent:@"fileName"];
  NSLog(@"path == %@",path);
  //Data to be written  NSString *temp = @"Hello world";
  int data0 = 1000000;
  float data2 = 23.23f;
  //Create data buffering  NSMutableData *writer = [[NSMutableData alloc]init];
  //Add string to buffer  [writer appendData:[temp dataUsingEncoding:NSUTF8StringEncoding]];
  [writer appendBytes:&data0 length:sizeof(data0)];
  [writer appendBytes:&data2 length:sizeof(data2)];
   
  [writer writeToFile:path atomically:YES];
  [writer release];
  
  //Read operation  int gData0;
  float gData1;
  NSString *gData2;
  
  NSData *reader = [NSData dataWithContentsOfFile:path];
  gData2 = [[NSString alloc]initWithData:[reader subdataWithRange:NSMakeRange(0, [temp length])] encoding:NSUTF8StringEncoding];
  [reader getBytes:&gData0 range:NSMakeRange([temp length], sizeof(gData0))];
  [reader getBytes:&gData1 range:NSMakeRange([temp length]+ sizeof(gData0) , sizeof(gData1))];
  NSLog(@"gData0 == %d",gData0);
  NSLog(@"gData1 == %f",gData1);
  NSLog(@"gData2 == %@",gData2);
  
  //  = gData2;
   
}

#import ""

@implementation ManagerFile

-(void)writeFile:(NSString *)file 
{ 
  //Create a file manager  NSFileManager *fileManager = [NSFileManager defaultManager]; 
  //Get the path  //What kind of path should I get from the NSDocumentDirectory parameter  NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); 
  NSString *documentsDirectory = [paths objectAtIndex:0];//The path required for the place  //Change to the directory to be operated  [fileManager changeCurrentDirectoryPath:[documentsDirectory stringByExpandingTildeInPath]]; 
  //Create file fileName file name, contents file contents, if there is no content at the beginning, it can be set to nil, attributes file attributes, initially nil  //Get file path  [fileManager removeItemAtPath:@"username" error:nil]; 
  NSString *path = [documentsDirectory stringByAppendingPathComponent:@"username"]; 
  //Create data buffering  NSMutableData *writer = [[NSMutableData alloc] init]; 
  //Add string to buffer  [writer appendData:[file dataUsingEncoding:NSUTF8StringEncoding]]; 
  //Add other data to buffer  //Write the buffered data into the file  [writer writeToFile:path atomically:YES]; 
  [writer release]; 
} 
-(NSString *)readFile 
{ 
  //Create a file manager  NSFileManager *fileManager = [NSFileManager defaultManager]; 
  //Get the path  //What kind of path should I get from the NSDocumentDirectory parameter  NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); 
  NSString *documentsDirectory = [paths objectAtIndex:0];//The path required for the place  //Change to the directory to be operated  [fileManager changeCurrentDirectoryPath:[documentsDirectory stringByExpandingTildeInPath]]; 
  //Get file path  NSString *path = [documentsDirectory stringByAppendingPathComponent:@"username"]; 
  NSData *reader = [NSData dataWithContentsOfFile:path]; 
  return [[NSString alloc] initWithData:reader 
                 encoding:NSUTF8StringEncoding]; 
} 
@end