How to write a file in IOS - objective-c

Question

I am new to IOS programming. I want to write some data into file. I have opened successfully the file in Document path. But fwrite its not working as expected. If I open the file its empty. Its my code I'm using. What I'm doing wrong.
typedef struct test {
int a;
} TEST_OBJ;
TEST_OBJ test_obj1;
test_obj1.a = 5;
TEST_OBJ *data_ptr = &test_obj1;
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *appFile = [documentsDirectory stringByAppendingPathComponent:#"MyFile1.txt"];
//This is working fine.
// [data writeToFile:appFile atomically:YES];
NSFileManager *fileManager = [[NSFileManager alloc]init];
char const *path = [fileManager fileSystemRepresentationWithPath:appFile];
FILE *fp = fopen(path, "w+b");
// This write is not working. File is empty.
int cnt = fwrite (data_ptr , 1 , sizeof(test_obj1) , fp );
fclose(fp);
fp = NULL;
Anyone pls tell me what I'm doing wrong?

Answer 1

I recommend you use NSData instead of C functions.
NSData *myData = [[NSData alloc] initWithBytes:bytes length:length];
[myData writeToFile:path atomically:YES];

Answer 2

you can use NSData,NSArray,NSDictionary,they have [writeToFile: atomically:] method ,it can write the data into the file.
if you must C to read and write filestream,you can use my method below , it can add arrayString to the file .
- (void)putArrayString:(NSString *)arrayString toFilePath:(NSString *)filePath
{
FILE *fileStream = fopen([filePath UTF8String], "a+");
if(fileStream == NULL)
{
fclose(fileStream);
fileStream = fopen([filePath UTF8String], "w+");
fputs([arrayString UTF8String], fileStream);
}
else
{
fputs([arrayString UTF8String], fileStream);
}
fclose(fileStream);
}

Answer 3

I have changed the mode of opening a+ its writing and reading properly now. Thanks all for your help.

Answer 4

See if you can use this code:
https://github.com/RIKSOF/three20/blob/master/src/extThree20RemoteObject/Source/TTObjectModel.m
Start reading from the encodeToDocument method. It writes all properties of an object in to a JSON or XML file.
Any subclass of this class having any property is properly written back.