We are implementing SQLite in iOS, in Swift, without using wrappers or Objective-C bridging. Everything works fine, except when doing a query and extracting the result. The issue is with the UnsafePointer<UInt8> that is returned from SQLite in Swift as follows:
var querySQL = "SELECT address, phone FROM CONTACTS WHERE NAME = 'myName'"
var cQuery = querySQL.cStringUsingEncoding(NSUTF8StringEncoding)
var statement: COpaquePointer = nil
if sqlite3_prepare_v2(contactsDB, cQuery!, -1, &statement, nil) == SQLITE_OK {
if sqlite3_step(statement) == SQLITE_ROW {
var address : UnsafePointer<UInt8> = sqlite3_column_text(statement, 0)
var data = NSData(bytes: address, length: 10)
var string = NSString(data: data, encoding: NSUTF8StringEncoding)
println(string)
As you can see, we can convert the pointer to String if we know the length of the object (in this case 10)
To dig into this issue, I have the following example
let pointerFromString: UnsafePointer<Int8> = "xyz".cStringUsingEncoding(NSUTF8StringEncoding)
let stringFromPointer = String.fromCString(anotherPointerFromString_Int8) println(stringFromPointer!)
Given that CChar is an alias of Int8, I can convert a String to UnsafePointer<Int8> using .cStringUsingEncoding(), and then back to String using .fromCString(<UnsafePointer_CChar>)
The problem is that my SQLite result is a UnsafePointer_UInt8, that can´t be used with .fromCString()
The bottom line question is: Is it possible to convert or cast a UnsafePointer_UInt8 to UnsafePointer_Int8
This should work:
let address = sqlite3_column_text(statement, 0)
let string = String.fromCString(UnsafePointer<CChar>(address))
Update for Swift 3 (Xcode 8), compare Swift 3: convert a null-terminated UnsafePointer<UInt8> to a string:
let string = String(cString: sqlite3_column_text(statement, 0))
Update:
sqlite3_column_text() returns an implicitly unwrapped optional, and that is why you can pass it to String(cString:) directly.
But according to Column methods, error and NULL handling #41, the return value can be null (in an out-of-memory situation, or if called with a NULL column type). Therefore it is safer to do
if let text = sqlite3_column_text(statement, 0) {
let string = String(cString: text)
// ...
} else {
// sqlite3_column_text() returned NULL
}
Related
We are implementing SQLite in iOS, in Swift, without using wrappers or Objective-C bridging. Everything works fine, except when doing a query and extracting the result. The issue is with the UnsafePointer<UInt8> that is returned from SQLite in Swift as follows:
var querySQL = "SELECT address, phone FROM CONTACTS WHERE NAME = 'myName'"
var cQuery = querySQL.cStringUsingEncoding(NSUTF8StringEncoding)
var statement: COpaquePointer = nil
if sqlite3_prepare_v2(contactsDB, cQuery!, -1, &statement, nil) == SQLITE_OK {
if sqlite3_step(statement) == SQLITE_ROW {
var address : UnsafePointer<UInt8> = sqlite3_column_text(statement, 0)
var data = NSData(bytes: address, length: 10)
var string = NSString(data: data, encoding: NSUTF8StringEncoding)
println(string)
As you can see, we can convert the pointer to String if we know the length of the object (in this case 10)
To dig into this issue, I have the following example
let pointerFromString: UnsafePointer<Int8> = "xyz".cStringUsingEncoding(NSUTF8StringEncoding)
let stringFromPointer = String.fromCString(anotherPointerFromString_Int8) println(stringFromPointer!)
Given that CChar is an alias of Int8, I can convert a String to UnsafePointer<Int8> using .cStringUsingEncoding(), and then back to String using .fromCString(<UnsafePointer_CChar>)
The problem is that my SQLite result is a UnsafePointer_UInt8, that can´t be used with .fromCString()
The bottom line question is: Is it possible to convert or cast a UnsafePointer_UInt8 to UnsafePointer_Int8
This should work:
let address = sqlite3_column_text(statement, 0)
let string = String.fromCString(UnsafePointer<CChar>(address))
Update for Swift 3 (Xcode 8), compare Swift 3: convert a null-terminated UnsafePointer<UInt8> to a string:
let string = String(cString: sqlite3_column_text(statement, 0))
Update:
sqlite3_column_text() returns an implicitly unwrapped optional, and that is why you can pass it to String(cString:) directly.
But according to Column methods, error and NULL handling #41, the return value can be null (in an out-of-memory situation, or if called with a NULL column type). Therefore it is safer to do
if let text = sqlite3_column_text(statement, 0) {
let string = String(cString: text)
// ...
} else {
// sqlite3_column_text() returned NULL
}
We are implementing SQLite in iOS, in Swift, without using wrappers or Objective-C bridging. Everything works fine, except when doing a query and extracting the result. The issue is with the UnsafePointer<UInt8> that is returned from SQLite in Swift as follows:
var querySQL = "SELECT address, phone FROM CONTACTS WHERE NAME = 'myName'"
var cQuery = querySQL.cStringUsingEncoding(NSUTF8StringEncoding)
var statement: COpaquePointer = nil
if sqlite3_prepare_v2(contactsDB, cQuery!, -1, &statement, nil) == SQLITE_OK {
if sqlite3_step(statement) == SQLITE_ROW {
var address : UnsafePointer<UInt8> = sqlite3_column_text(statement, 0)
var data = NSData(bytes: address, length: 10)
var string = NSString(data: data, encoding: NSUTF8StringEncoding)
println(string)
As you can see, we can convert the pointer to String if we know the length of the object (in this case 10)
To dig into this issue, I have the following example
let pointerFromString: UnsafePointer<Int8> = "xyz".cStringUsingEncoding(NSUTF8StringEncoding)
let stringFromPointer = String.fromCString(anotherPointerFromString_Int8) println(stringFromPointer!)
Given that CChar is an alias of Int8, I can convert a String to UnsafePointer<Int8> using .cStringUsingEncoding(), and then back to String using .fromCString(<UnsafePointer_CChar>)
The problem is that my SQLite result is a UnsafePointer_UInt8, that can´t be used with .fromCString()
The bottom line question is: Is it possible to convert or cast a UnsafePointer_UInt8 to UnsafePointer_Int8
This should work:
let address = sqlite3_column_text(statement, 0)
let string = String.fromCString(UnsafePointer<CChar>(address))
Update for Swift 3 (Xcode 8), compare Swift 3: convert a null-terminated UnsafePointer<UInt8> to a string:
let string = String(cString: sqlite3_column_text(statement, 0))
Update:
sqlite3_column_text() returns an implicitly unwrapped optional, and that is why you can pass it to String(cString:) directly.
But according to Column methods, error and NULL handling #41, the return value can be null (in an out-of-memory situation, or if called with a NULL column type). Therefore it is safer to do
if let text = sqlite3_column_text(statement, 0) {
let string = String(cString: text)
// ...
} else {
// sqlite3_column_text() returned NULL
}
As the title says, what is the correct way to convert UnsafeMutablePointer to String in swift?
//lets say x = UnsafeMutablePointer<Int8>
var str = x.memory.????
I tried using x.memory.description obviously it is wrong, giving me a wrong string value.
If the pointer points to a NUL-terminated C string of UTF-8 bytes, you can do this:
import Foundation
let x: UnsafeMutablePointer<Int8> = ...
// or UnsafePointer<Int8>
// or UnsafePointer<UInt8>
// or UnsafeMutablePointer<UInt8>
let str = String(cString: x)
Times have changed. In Swift 3+ you would do it like this:
If you want the utf-8 to be validated:
let str: String? = String(validatingUTF8: c_str)
If you want utf-8 errors to be converted to the unicode error symbol: �
let str: String = String(cString: c_str)
Assuming c_str is of type UnsafePointer<UInt8> or UnsafePointer<CChar> which is the same type and what most C functions return.
this:
let str: String? = String(validatingUTF8: c_str)
doesn't appear to work with UnsafeMutablePointer<UInt8>
(which is what appears to be in my data).
This is me trivially figuring out how to do something like the C/Perl system function:
let task = Process()
task.launchPath = "/bin/ls"
task.arguments = ["-lh"]
let pipe = Pipe()
task.standardOutput = pipe
task.launch()
let data = pipe.fileHandleForReading.readDataToEndOfFile()
var unsafePointer = UnsafeMutablePointer<Int8>.allocate(capacity: data.count)
data.copyBytes(to: unsafePointer, count: data.count)
let output : String = String(cString: unsafePointer)
print(output)
//let output : String? = String(validatingUTF8: unsafePointer)
//print(output!)
if I switch to validatingUTF8 (with optional) instead of cString, I get this error:
./ls.swift:19:37: error: cannot convert value of type 'UnsafeMutablePointer<UInt8>' to expected argument type 'UnsafePointer<CChar>' (aka 'UnsafePointer<Int8>')
let output : String? = String(validatingUTF8: unsafePointer)
^~~~~~~~~~~~~
Thoughts on how to validateUTF8 on the output of the pipe (so I don't get the unicode error symbol anywhere)?
(yes, I'm not doing proper checking of my optional for the print(), that's not the problem I'm currently solving ;-) ).
whole code is like this:
var inputStream :NSInputStream?
var outputStream:NSOutputStream?
NSStream.getStreamsToHostWithName(ip, port: port, inputStream: &inputStream, outputStream: &outputStream)
let reader = inputStream
let writer = outputStream
writer?.open()
reader?.open()
var message : UInt8 = 0
while reader!.read(&message, maxLength: 1)>0
{
let wa = NSString(bytes: &message, length: 1, encoding: CFStringConvertEncodingToNSStringEncoding(CFStringEncoding(CFStringEncodings.GB_18030_2000.rawValue))) as! String
}
when the message i receive is a chinese character, the last line throws this:
fatal error:unexpected found nil while unwrapping an optional value, at the mean time, the value of message is 196
does anybody know how to solve this problem?
According to this page, if the byte you read is in the range 0x81-0xfe, the character is encoded using two or four bytes, so trying to decode just the first byte will fail. The NSString constructor will return nil, and attempting to unwrap it (with as! String) will throw that error.
You need to check what byte you read, and read another byte if necessary based on the first byte. Then you need to check the second byte, and possible read two more bytes. Finally, you need to pass all of the one, two, or four bytes to the NSString constructor in a single buffer.
Try to change message type for inputData like this for example:
let queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)
dispatch_async(queue) {
let bufferSize = 1024
var message = Array<UInt8>(count:bufferSize, repeatedValue: 0)
while true {
let bytesRead = self.inputStream!.read(&message, maxLength: bufferSize)
let responseString = NSString(bytes: message, length: message.count, encoding: NSUTF8StringEncoding) as! String
// Do somthing with response
...
}
}
In objective c, I use fscanf to read stream from file and assign the value to variables:
int count;
char type[5];
fscanf(myFile, “count is %d, type is %4s ”, &count, type)
I want to do the same thing in swift code, I tried:
//ERROR: Type annotation missing in pattern
//What type should I use for `count`?
var count
//ERROR: consecutive statement on a line must be separated by ‘;’
var type[5] : char
fscanf(myFile, “count is %d, type is %4s ”, &count, type)
But I got compiler errors showing above. What is the correct way to use fscanf in swift ?
If you know any swift way to achieve the same thing (without using fscanf), it would be great too!
I recommend you use Foundation framework solution for reading/writing file data. A sample code to read contents of files which I used in my app to stream file into NSData:
if let fileHandle = NSFileHandle(forReadingAtPath: "path/to/file") {
fileHandle.seekToFileOffset(0)
var data = fileHandle.readDataOfLength(5)
var chars = [UInt8](count: 5, repeatedValue: 0)
data.getBytes(&chars, length: 5)
fileHandle.closeFile()
}
In case you need read Int64 data from file at a specific location:
if let fileHandle = NSFileHandle(forReadingAtPath: "path/to/file") {
fileHandle.seekToFileOffset(0)
var data = fileHandle.readDataOfLength(500)
var intFetched: Int64 = 0
let location = 100 // start at 101st character of file
data.getBytes(&intFetched, range: NSMakeRange(location, 8))
println(intFetched.littleEndian)
fileHandle.closeFile()
}