CFDataAppend

CFDataAppend is a function within the Core Foundation framework in Apple's operating systems, including macOS and iOS. Its primary purpose is to append data from one byte buffer to another existing data buffer. This function is part of the CFData collection type, which represents immutable sequences of bytes.

The function signature for CFDataAppend is typically CFDataAppend(CFMutableDataRef theData, const void *bytes, CFIndex length). Here, theData refers to a mutable CFData object to which data will be appended. The bytes parameter points to the memory location containing the data to be added, and length specifies the number of bytes to append from that location.

When CFDataAppend is called, it dynamically resizes the mutable data buffer if necessary to accommodate the new data. The bytes from the specified memory location are then copied and added to the end of the existing data within theCFMutableDataRef object. This operation is fundamental for building up data structures or processing streams of information where the final size is not known in advance.

It's important to note that CFDataAppend operates on CFMutableDataRef, which is a mutable variant of CFData. This distinction is crucial because CFData itself is immutable, meaning its contents cannot be changed after creation. Therefore, to use CFDataAppend, one must first create a mutable data object using functions like CFDataCreateMutable.