How to convert NSData to byte array in iPhone

Question

I want to convert NSData to a byte array  so I write the following code   NSData  data    NSData dataWithContentsOfFile filePath   int len    data length   Byte byteData len   byteData    data bytes     But the last line of code pops up an error saying  incompatible types in assignment   What is the correct way to convert the data to byte array then

User · Answer

That s because the return type for  data bytes  is a void  c-style array  not a Uint8  which is what Byte is a typedef for     The error is because you are trying to set an allocated array when the return is a pointer type  what you are looking for is the getBytes length  call which would look like    data getBytes  amp byteData length len     Which fills the array you have allocated with data from the NSData object

User · Answer

You could also just use the bytes where they are  casting them to the type you need   unsigned char  bytePtr    unsigned char    data bytes

User · Answer

The signature of - NSData bytes  is -  const void   bytes  You can t assign a pointer to an array on the stack   If you want to copy the buffer managed by the NSData object into the array  use - NSData getBytes     If you want to do it without copying  then don t allocate an array  just declare a pointer variable and let NSData manage the memory for you

User · Answer

Already answered  but to generalize to help other readers         Here    NSData   fileData      uint8 t   bytePtr    uint8 t      fileData bytes           Here  For getting individual bytes from fileData  uint8 t is used         You may choose any other data type per your need  eg  uint16  int32  char  uchar               Make sure  fileData has atleast number of bytes that a single byte chunk would need  eg  for int32  fileData length must be  gt  4 bytes  Makes sense           Now  if you want to access whole data  fileData  as an array of uint8 t     NSInteger totalData    fileData length    sizeof uint8 t        for  int i   0   i  lt  totalData  i                   NSLog   data byte chunk    x   bytePtr i

User · Answer

You can t declare an array using a variable so Byte byteData len   won t work  If you want to copy the data from a pointer  you also need to memcpy  which will go through the data pointed to by the pointer and copy each byte up to a specified length    Try   NSData  data    NSData dataWithContentsOfFile filePath   NSUInteger len    data length   Byte  byteData    Byte  malloc len   memcpy byteData   data bytes   len     This code will dynamically allocate the array to the correct size  you must free byteData  when you re done  and copy the bytes into it   You could also use getBytes length  as indicated by others if you want to use a fixed length array  This avoids malloc free but is less extensible and more prone to buffer overflow issues so I rarely ever use it

User · Answer

Here s what I believe is the Swift equivalent   if let data   NSData contentsOfFile  filePath       let length   data length    let byteData   malloc length     memcmp byteData  data bytes  length

[iphone] How to convert NSData to byte array in iPhone?

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