CFDataReplaceBytes

CFDataReplaceBytes is a function provided by the Core Foundation framework in Apple's operating systems, including macOS, iOS, watchOS, and tvOS. This function is used to modify the contents of a CFMutableData object by replacing a specified range of bytes with new data.

The function signature is CFDataReplaceBytes(CFMutableDataRef data, CFRange range, const UInt8 *replacementBytes, CFIndex replacementLength). The first parameter, data, is a pointer to the mutable data object that will be modified. The second parameter, range, specifies the starting byte offset and the number of bytes within the data object to be replaced. The third parameter, replacementBytes, is a pointer to the array of bytes that will replace the specified range. The final parameter, replacementLength, indicates the number of bytes in the replacement data.

When CFDataReplaceBytes is called, the bytes in the data object from the start of the specified range up to the specified length are removed. Then, the replacementBytes are inserted at that same location. If the replacementLength is different from the length of the range being replaced, the overall length of the CFMutableData object will change accordingly. This function is a fundamental operation for manipulating binary data within the Core Foundation ecosystem. It is often used in conjunction with other CFData functions to build, parse, or modify data buffers.