how to overcome this error
func selectFunc(){
var selectQuery="select * from EmployeInfo"
var cSql:CString = selectQuery.bridgeToObjectiveC().cStringUsingEncoding(NSUTF8StringEncoding)
var result:CInt=0
var stmt:COpaquePointer = nil
result = sqlite3_prepare_v2(appDelegate.database, cSql, -1, &stmt, nil);
if result != SQLITE_OK
error occurred use of undeclared CString.how to overcome this error
In older Swift versions (before Xcode 6 beta 6), a Swift String had explicitly to be converted
when passed to a C function taking a const char * argument, as in your code.
This is no longer necessary. The CString type and the bridgeToObjectiveC() method do not exist anymore.
The current Swift compiler does the conversion
automatically (compare String value to UnsafePointer<UInt8> function parameter behavior) and you can just write
let selectQuery = "select * from EmployeInfo"
var stmt : COpaquePointer = nil
let result = sqlite3_prepare_v2(appDelegate.database, selectQuery, -1, &stmt, nil)
Related
Does someone know what goes I'm doing wrong here?
// ...
val alphabet = ('a'..'z').toList()
val str = "testing"
val arr = str.split("")
for (char in arr) {
var i = alphabet.indexOf(char) // Throws Error!
// ...
}
The indexOf-method results in
"Error:(10, 26) Kotlin: Type inference failed. The value of the type parameter T should be mentioned in input types (argument types, receiver type or expected type). Try to specify it explicitly."
I have tried to "var i: Int = alphabet.indexOf(char)" and "alphabet.indexOf(char) as Int". The same result ...
What's the issue here?
I believe that your problem is that you think that the variable char contains a Char value. If that were the case, then it would make sense for indexOf to be accepting a Char value and then finding the location of that character in a list of characters (List<Char>) on which the method is being called.
But str.split() is returning a List<String>, not a List<Char>, and so char is a String. So you are asking the indexOf method to tell you the location of a String in a list of characters (List<Char>). That doesn't make sense. That's the basis of the problem. Exactly how that translates to the error you're getting from the Kotlin compiler, I'm not sure.
To make it clear, this line produces the same error:
var i = alphabet.indexOf("c") // Throws Error!
but the compiler likes this line just fine:
var i = alphabet.indexOf('c') // No Error!!!
I'm new to Objective-C so I don't have much idea about the language.
What I'm trying to do is go through all available instance methods of an object and call the ones that take no arguments, return bool and start with the string "func".
Here's how I get the methods:
uint32_t methodCount = 0;
Method * methods = class_copyMethodList(object_getClass(self), &methodCount);
I iterate through the methods and when the above condition matches, try to call them:
NSString * methodName = [NSString stringWithUTF8String:sel_getName(method_getName(method))];
char retTyp[10];
method_getReturnType(method, retTyp, 10);
const char * desiredRetType = "B";
if([methodName hasPrefix:#"func"] &&
(0 == strncmp(retTyp, desiredRetType, strlen(desiredRetType))) &&
(2 == method_getNumberOfArguments(method)))
{
bool * (* testMethod) (id, Method) = (void (*) (id, Method, ...)) method_invoke;
result = testMethod(self, method);
}
I had to experimentally figure out what the return type string is (turns out it's "B" for bool), and the number of arguments.
I'm getting the following error on the line where I'm trying to call the function using method_invoke:
cannot initialize a variable of type 'bool *(*)(__strong id, Method)' (aka 'bool *(*)(__strong id, objc_method *)') with an rvalue of type 'void (*)(__strong id, Method, ...)' (aka 'void (*)(__strong id, objc_method *, ...)'): different return type ('bool *' vs 'void')
Is there a better way to way to do this than class_copyMethodList?
How do I cast the function correctly so as to not get an error?
Is it possible that the method_getReturnType() conversion of return
types may change from system to system? Or is it always B for bool?
NVM, I figured it out. Instead of using method_invoke on the method name, I did this:
NSString * methodName = [NSString stringWithUTF8String:sel_getName(method_getName(method))];
char retTyp[10];
method_getReturnType(method, retTyp, 10);
const char * desiredRetType = "B";
if([methodName hasPrefix:#"func"] &&
(0 == strncmp(retTyp, desiredRetType, strlen(desiredRetType))) &&
(2 == method_getNumberOfArguments(method)))
{
SEL testMethod = method_getName(method);
return [self performSelector:testMethod];
}
I am attempting to run a conditional to basically see if the object is empty but I keep getting (similar variations) of this error:
invalid operation: release.Name == "" (mismatched types *string and string)
Here is the code that is dying:
import (
"github.com/google/go-github/github"
)
func TestLatestTag(user, project string) {
var client *github.Client
client = github.NewClient(nil)
releases, _, err := client.Repositories.ListTags(user, project, nil)
var release github.RepositoryTag
if err != nil {
fmt.Println("Error")
} else {
if release.Name == "" {
fmt.Println("None")
} else {
fmt.Println(releases[0])
}
}
}
If I change the if statement to *release.Name == "" as the error suggests I get a different error, which I don't really understand:
panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xb code=0x1 addr=0x0 pc=0x26fd]
goroutine 1 [running]:
I'm sure there is any easy way to do this but I am not very familiar with handling objects/structs
From the error message it looks like you are trying to compare a string pointer (*string) to an actual string.
release.Name is a *string (a pointer to a string value)
"" is a string (is a string value)
They are two different types. So you can't compare them.
What you probably want to do instead is release.Name == nil
When a pointer that references to nothing (equals to nil) is tried to be dereferenced you get that second error. So in your case *release.Name panics because infact release.Name is nil
var release github.RepositoryTag
You never assign any value to that var. That's why *release.Name gives you a "runtime error": release.Name is a nil pointer
As per your code you have declared var release github.RepositoryTag, but you have not initialized it.
In structure RepositoryTag, Name is declared as *string which is a pointer and in case of release.Name == "", string comparison is attempted which is incorrect hence "mismatched types *string and string" error.
In case of *release.Name == "", since release is not yet initialized, it is complaining "invalid memory address or nil pointer dereference"
You need to do two things, 1st initialize, release and second, check release.Name = nil.
Im trying to do the following in Swift:
CFArrayRef attachmentsArray = CMSampleBufferGetSampleAttachmentsArray(sampleBuffer, 0);
if (CFArrayGetCount(attachmentsArray)) {
CFBooleanRef notSync;
CFDictionaryRef dict = CFArrayGetValueAtIndex(attachmentsArray, 0);
BOOL keyExists = CFDictionaryGetValueIfPresent(dict,
kCMSampleAttachmentKey_NotSync,
(const void **)¬Sync);
I have:
if CFArrayGetCount(attachmentsArray) != 0 {
let dict = CFArrayGetValueAtIndex(attachmentsArray, 0)
However, dict is a UnsafePointer instead of a dictionary like it should be. When I printed attachmentsArray I got
Optional({ DependsOnOthers = 0; })
I tried casting it to a CFDictionaryRef but it would fail in runtime.
How do I succeed in doing the above Obj-C code in Swift?
However, dict is a UnsafePointer instead of a dictionary like it should be.
No, not "like it should be". Look at the declaration:
func CFArrayGetValueAtIndex(theArray: CFArray!, _ idx: CFIndex)
-> UnsafePointer<Void>
It returns an UnsafePointer-to-void because that is what it is supposed to do. (In Objective-C it returns a const void *.)
I was pointed to this objc snippet from WWDC 14, but I work on a Swift project.
CMIOObjectPropertyAddress prop = {
kCMIOHardwarePropertyAllowScreenCaptureDevices,
kCMIOObjectPropertyScopeGlobal,
kCMIOObjectPropertyElementMaster
};
UInt32 allow = 1;
CMIOObjectSetPropertyData(kCMIOObjectSystemObject, &prop, 0, NULL, sizeof(allow), &allow);
I then tried rewriting to Swift:
var prop : CMIOObjectPropertyAddress {
kCMIOHardwarePropertyAllowScreenCaptureDevices
kCMIOObjectPropertyScopeGlobal
kCMIOObjectPropertyElementMaster
}
var allow:UInt32 = 1
CMIOObjectSetPropertyData(kCMIOObjectSystemObject, &prop, 0, nil, sizeof(UInt32), &allow)
But it doesn't even validate. I don't know how to translate the CMIOObjectPropertyAddress struct. Xcode says
/Users/mortenjust/Dropbox/hack/learning/screenrec/screenrec/deleteme.swift:32:61:
Cannot assign to a get-only property 'prop'
A C struct translates as a Swift struct. Use the implicit memberwise initializer:
var prop = CMIOObjectPropertyAddress(
mSelector: UInt32(kCMIOHardwarePropertyAllowScreenCaptureDevices),
mScope: UInt32(kCMIOObjectPropertyScopeGlobal),
mElement: UInt32(kCMIOObjectPropertyElementMaster))
The cool part is when you type CMIOObjectPropertyAddress(, code completion gives you the rest.
You're right, just got it running right this second. Turns out I also had to correct for some of the types. Here's the complete translation:
var prop = CMIOObjectPropertyAddress(
mSelector: CMIOObjectPropertySelector(kCMIOHardwarePropertyAllowScreenCaptureDevices),
mScope: CMIOObjectPropertyScope(kCMIOObjectPropertyScopeGlobal),
mElement: CMIOObjectPropertyElement(kCMIOObjectPropertyElementMaster))
var allow : UInt32 = 1
var dataSize : UInt32 = 4
var zero : UInt32 = 0
CMIOObjectSetPropertyData(CMIOObjectID(kCMIOObjectSystemObject), &prop, zero, nil, dataSize, &allow)
var session = AVCaptureSession()
session.sessionPreset = AVCaptureSessionPresetHigh
var devices = AVCaptureDevice.devices()
for device in AVCaptureDevice.devices() {
println(device)
}