Weird behavior of fopen on ios - objective-c

Question

I am trying to create a file by fopen and then write it, but weird things happened.
When I plug in the iphone to the usb port. Everything works fine. A file is created at the tmp directory or the document directory as expected.
When I plug off the device and do the same thing, the file did not appear. I was wondering why.
I use fopen to create the file. In my case, I should do this to create and then write the file. The call is fopen(pcm_output, "wb+");

Answer 1

You need to use this call.
char const *path = [fileManager fileSystemRepresentationWithPath:url.path];
From the docs...
fileSystemRepresentationWithPath:
- (const char *)fileSystemRepresentationWithPath:(NSString *)path
iOS (2.0 and later)
Returns a C-string representation of a given path that properly encodes Unicode strings for use by the file system.
path: A string object containing a path to a file.
A C-string representation of path that properly encodes Unicode strings for use by the file system.

Answer 2

You're probably writing outside of the sandbox, can you post the path?
Just as a test try to turn on iTunes Sharing (this should have no effect, it's just a test) for your app.
EDIT:
After testing I discovered that you have to use:
NSString *docsPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
NSString *filePath = [docsPath stringByAppendingPathComponent:[NSString stringWithCString:pcm_output encoding:NSUTF8StringEncoding]];
fopen([filePath UTF8String], "wb+");
Instead of just:
fopen([filePath UTF8String], "wb+");

Answer 3

NSArray *paths = NSSearchPathForDirectoriesInDomains(
NSDocumentDirectory,
NSUserDomainMask, YES
);
NSString* docDir = [paths objectAtIndex:0];
_tempLogPath = [docDir stringByAppendingPathComponent: #"Aisound5_CBLog.log"];
_tempPcmPath = [docDir stringByAppendingPathComponent: #"OutPcm.pcm"];
_tempWavPath = [docDir stringByAppendingPathComponent: #"OutWav.wav"];
tts_resource = [[bundle pathForResource:#"Resource_dev" ofType:#"irf"] UTF8String];
tts_log = [_tempLogPath UTF8String];
pcm_output = [_tempPcmPath UTF8String];
wav_output = [_tempWavPath UTF8String];
The original code is this, in which tts_resource tts_log pcm_output and wav_output are defined in a .h file and used in a .c file with fopen.
I had tried in your way to init the const string with the explicit const char* style, but the problem remains the same.