![]() ![]() The way to get a C string pointer from a Swift String is the withCString method that'll give you a (temporary) UnsafePointer.You may also need to add some amount of optionality to get the type you want. CChar is the Swift type equivalent to char, not char** you need UnsafeMutablePointer> (or just UnsafeMutablePointer> if it should really be const char **, or UnsafePointer> if it should really be const char * const *).The low-level answers to your question are that: I agree with Quinn that it would be better to get a prototype for your function by importing a C header instead of trying to declare the function type in Swift. What’s the memory management for the ‘returned’ C string? Here I’m doing nothing with it, but it’s possible that you might need to free it. Is it safe to look at the error regardless of the function result? The standard Cocoa convention is that you should ignore an indirect error like this if the function succeeds. Let errorStr = String(cString: errorCStr) If so, you might write the code like this: var errorCStrQ: UnsafeMutablePointer? = nil It looks like the second parameter is a way for the C function to return you an error string. Thus, I added a prototype like this to my bridging header: extern int something(int somethingElse, char **errorStringPtr) įinally, it’s hard to give a definitive answer because pointer-to-pointer-to-char can have lots of different semantics in C. That allows you to focus on the pointer-to-pointer-to-char problem, and leave the function pointer issues for later. Rather, start by declaring your function in C and then accessing it via a bridging header. Next, I recommend that you temporarily avoid dealing with function pointers. Your question is about how to achieve something in Swift as it currently stands, and that’s perfect for the Using Swift area. You should study the demonstration programs in conjunction with this module.First up, if there’s a way you to move your thread over to Using Swift, you should do so. The both say, "The name of an array is a pointer take the pointer and calculate a new address that points to the 3 rd offset by adding the correct number of bytes onto the pointer (integer data type is normally 4 bytes long – 3 offsets times 4 bytes is 12 bytes) then dereference that pointer (since this is an Rvalue context – fetch me the value that you are pointing at) and send it to the standard output device." ![]() The array index operator is also known as the array method of dereferencing. The use of pointers with indirection is often preferred for processing arrays. The above example shows the basic mechanics of the indirection operator. Note: The asterisk and must appear in both the prototype and the function definition when defining the pointer variables but it does not appear in the function call when the pointers are passed into the function. Void process_values(int qty_dimes, int qty_quarters, double *ptr_value_dimes, double *ptr_quarters) Process_values(dimes, quarters, ptr_value_dimes, ptr_value_quarters) Void process_values(int qty_dimes, int qty_quarters, double *ptr_value_dimes, double *ptr_value_quarters) ĭouble *ptr_value_quarters = &value_quarters The concept of indirection is also known as dereferencing, meaning that we are not interested in the pointer but want the item to which the address is referring or referencing. The indirection operator is the asterisk or the character that we also use for multiplication. Although different syntax than parameter passing when using a reference variable using a pointer variable and the indirection operator can accomplish the same effect. These exceptions could be handled by parameter passing by reference instead of passing a value. When a copy of an argument cannot reasonably or correctly be made (example: file stream objects). When we need more than one item of information returned by the function This has the advantage of a closed communications model with everything being neatly passed in as values and any needed item returned back as a parameter.īy necessity there are two exceptions to this closed communications model: The called function passes back a single value as the return item if needed. ![]() This is the preferred method when calling user defined specific task functions. The called function takes these values which have local scope and stores them on the stack using them as needed for whatever processing the functions accomplishes. ![]() When we pass parameters to functions we usually pass by value that is the calling function provides several values to the called function as needed. ![]()
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