Reference through null fortran pointer

FortsRaw is an attempt to provide a set of generic containers for Fortran that are typical and common in the STL. So far only a linked list is there but in follow up posts I will add hash tables, vector like containers using macro preprocessor tricks to provide primative templates in Fortran. For a quick benchmark on my machine here are some quick results. The append times make sense - 10 X the number of elements to append 10 X the time taken. The get method however, was done on each element and shows how computational bad it is to access an element by index when using a linked list.

After 10, entries it becomes unfeasible to access the elements. Not good. Please refrain from using linked lists in Fortran, they rarely are the correct data structure. This was put here as an academic exercise only to show you how bad they are. They also cannot be vectorized! Oh and of course this needs unit testing, which has been done on that repository. TOAST will be the subject of another post too.

Written by Thomas Stainer who likes to develop software for applications mainly in maths and physics, but also to solve everyday problems. Check out my GitHub page here. Home About.

Note - do not copy lists, i. Although the Kotlin types have been specified to help with this, in practice they would usually be omitted and inferred by the compiler.

Lua does not have pointers but it is worth remembering that assigning a table to a new variable creates a reference to that table, not a copy of it. There are three kind of pointers, and two kind of references.

Pointers can change, but reference can't change. There are no arithmetic operations to pointers. We can operate for objects that points. References are never nil, but weak references maybe invalid.

There is a special container an object named Buffer for handling memory blocks and we can get addresses from that and use them to call code we can make memory blocks for code execution too. So using buffers for data and buffers for code we can use pointers as those in assembly. Also we can use external dll, and pass them addresses too. Read Statement get a weak reference and make it a normal reference.

Variable X can't get new reference. We can't get reference from an item in a container array, inventory, stack. Every time we use the string as weak reference, interpreter make resolve to reference. We can declare objects Com type and we get a pointer, but that pointer leave until the end of module, which we create the pointer. We may declare properties for these objects, and also that properties use smart pointers, so the com object has only one pointer, which deleted at the exit of module where created.

Com objects are internal GUI objects. We use Method to call methods and return values. We can use With to read, set values, and to bound properties to names. We can use Nothing to delete objects names can't get another object , it is optional, but has to do with the release of resource, and when happen.

For forms it is better to use it as in the example below. There are three containers, Arrays, Inventories and Stacks. Arrays have two interfaces, the value one and the pointer one. The value one has parenthesis in the name. Containers may have items other containers. Usually containers combined with functions and statements, but because they are COM objects but pointers inside work different from other Com objects , we can use statemends Method and With as for com objects.

Groups are value types, but we can make pointers for them. Assigning a Group to a Group we get a combination, the group at the left get all the members of the group at the right except the situation we have define a Set function for Group, and handle the assignment as we wish, or not defined it but define a value function so interpreter treat it as read only and throw error.

Modula-3 uses references; However, it does allow arithmetic and address operations but only in unsafe modules. There are two reference types in Modula-3, traced and untraced.

Traced reference types are garbage collected, whereas untraced reference types are not. Address arithmetic and address operations are allowed only on untraced reference types. Untraced references are only allowed in unsafe modules. Like Java, Python, and most other languages, many complex data structures in OCaml are boxed, including records, arrays, objects, algebraic data types, etc. In other words, you always refer to them using a level of indirection.

Records and objects can contain mutable fields, and elements of arrays are mutable. So when you pass a mutable record or array, you are actually passing a reference and the contents of the record or array can be modified by the called function. If you just want a simple mutable "variable" since variables in OCaml are immutable , you can allocate a reference a simple mutable data structure with one field; not the same meaning as the "references" in other languages with an initial value, read from it, and write to it:.

The OCaml web-site provides this page on the subject. The data stack only holds references to objects. When you use dup, swap, over, When an object is sent as a parameter to a function or method, its reference is sent. If the object is a mutable object, the function can modify this object. In ooRexx, all values are references to an object. When passing arguments, you are passing object references by value.

So if you want to reflect changes in an argument back to the caller, one thing that you can do is wrap the argument as an attribute of an object, then modify the object through the reference. With the Use Arg instruction, a subroutine get access to the caller's argument object by reference:. User functions and certain built-in functions listput, listpop, mapput, etc.

Pari program can use C pointers normally. In fact, all GEN variables are actually pointers to a space within the Pari stack or, rarely, the Pari heap.

Perl has "references" that roughly correspond with "smart pointers" of C-like languages. Due to reference-counting semantics, they can never point to something that does not exist. Any scalar container which includes array elements and hash values, but not hash keys can hold a reference to a data structure. There is no pointer math beyond sizes in bytes. There are in fact 5 variants of poke: poke1, poke2, poke4, poke8, and pokeN which allows the size to be dynamically specified.

Likewise there are 9 versions of peek: peek1s, peek2s, peek4s, peek8s, peek1u, peek2u, peek4u, peek8u, and peekNS, and again the latter allows the size and signed flag to be dynamically specified. Of course in a reference counted language like Phix, playing directly with the innards like that may have dire unexpected side effects.

Phix does not have references, however everything is passed by reference, with copy-on-write semantics. Unless the source and destination are the same, and it is local, so it cannot possibly be referenced elsewhere, in which case automatic pass-by-reference is used, which for Phix means skipping the reference counting.

For example:. It is a general optimisation, applied by the complier whenever and wherever it can, without the programmer having to do anything special. Phix takes the view that there should be as few as possible unintended side effects. Personally I find that approach often helps me narrow down all the places where a bug might lurk much quicker, and that is certainly worth an occasional bit of extra typing on the lhs. There is an extreme example in the interpreter. For performance, symtab names are left as a meaningless to a human ternary tree index, until an error occurs.

At which point pEmit2. It ain't pretty but it works well. In most cases, PHP "does the right thing" as pertaining to variables and not duplicating variables in memory that have not been edited.

So, in the above functions example, if we took out all the ampersands, it would all work perfectly and not duplicate the big string in memory up until the line where we concatenate and add "EDIT" to the end. PHP Objects are Always passed by reference, so passing an object into and out of a function, will not make multiple cloned instances of that object.

However, arrays are Not objects, and thus, every time they are passed or copied, they need to be passed by reference if you mean for any changes on the child to be applied to the parent.

The internal PicoLisp machinery consists completely of pointers. Any data item except numbers is a pointer that points to a cell, which in turn consists of two pointers "cons pair". The pointers are not evident to the programmer. The development environment presents them as high level structures symbols or lists. Where is the problem?

I printed every variable to make sure everything works fine and it seems alright but I can't identify this error. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Asked 1 year ago. Active 1 year ago. Viewed times. Improve this question. Mahdi Julaye. Mahdi Julaye Mahdi Julaye 11 1 1 bronze badge. Mistakes in calls to these functions are very common. As explained above, a function's arguments are contained in a single SAI entry.

It is therefore easy for functions such as printf to report if too few arguments are supplied. A further problem with the traditional C system library, is that most error conditions for example a negative argument to sqrt are handled by setting the global variable errno and returning. Programs which do not check errno after every library function call which could set it i.

SCC provides a function which may be called to activate certain classes of error, such as arithmetic domain errors, so that the program fails after such an error and enters the debugger. It is possible for users to set up hopefully well tested libraries to operate in this way. This may be very valuable for general purpose class libraries.

Pointers to the virtual function table, and pointers to virtual base classes are set by the system only. Other objects, such as reference member variables, should not change their values after initialisation.

Currently the CHECK mechanism does not address these issues, except that it checks that the virtual function pointer points to a valid virtual function table before using it. In principle, the SAI entry for such a class could be split into several entries covering each user-accessible region, or some other scheme to restrict access to system parts of the object could be implemented.

Typically, he may allocate storage from a single large region of memory obtained from the system. Since in general it is important that a program executes in the same way in CHECK mode as it will in normal use, wise users will use this facility sparingly! SCC can handle inline bit Intel assembler. At first sight this poses serious problems in check mode. In particular, automatic objects that are moved to the heap see above require an extra level of indirection in order to access them. For example:.

This assembles as an LEA instruction, which loads the address of its operand, in normal mode, or if k does not require allocation on the heap, and as a MOV instruction accessing the pointer to k if k is allocated on the heap.

Pseudo instructions are also supplied to check the contents of a register to ensure that they point to a suitable SAI entry. These pseudo instructions assemble into code which preserves all registers over the check. In non-check mode these pseudo instructions generate no code. CHECK mode does not, of course, solve the problems caused by incorrect assembler code, which may still corrupt the system.

In designing the above checking mechanism considerable care was taken to avoid constructions which would have had unfortunate side-effects.

In particular, it was decided that:. Because of the above constraints it was decided that any attempt to detect uninitialised data using additional bits was impractical. Furthermore, it was decided that any attempt to validate a pointer reference using the past history of the pointer was impractical. Only by tracking the history of the pointer p would it be possible to fault this program in all cases.

As with FORTRAN 77, traditional C programs which do not use function prototypes can become corrupt if a function is called with the wrong number or types of arguments, or if the return type does not match. Floating point errors, such as overflow, can be detected by the hardware without special action by the compiler. In order to detect integer overflow, the compiler would have to plant extra instructions to check the condition codes.

Also, many programmers mix signed and unsigned data in ways which technically cause overflow. Since integer overflow is a much less serious problem in a 32 bit environment, it was decided not to attempt to detect this problem. On average, we find that a reduction of speed by a factor of 10 is common. CHECK mode programs also use much more memory. Since it is anticipated that CHECK mode will only be used as a debugging tool, this loss of performance should be acceptable except for those programs with a real-time component.

However, since some sources of program corruption - such as incorrect assembler code - may invalidate the assumptions which the compiler might use to make such optimisations, it is not clear whether this would be worthwhile.

These problems can be almost eliminated at debug-time by the use of suitable compilation techniques.