The existing relationship between c and language

Understanding the Differences Between C#, C++, and C - C# Station

the existing relationship between c and language

Both C and C++ give you a lower level of abstraction that, with increased . (The major difference between those languages being that C# is statically typed . its community (advice, but also existing code you can read and learn from) and the. Home» FAQ» What is the difference between C and C#?. With dozens of “C” family program languages in existence, it's easy to confuse them with each other . C is one of the oldest programming languages around. are also written in C. They are just mobile adaptations of existing Mac OS, Linux and Windows kernels.

For example, in this snippet: It's always possible that what you can find there is one Foo in a long sequence stuck end-to-end, so the language provides you with a convenient way to step back and forth along that sequence. Idiomatic C code will use this facility frequently. String handling code in particular which we'll examine in more detail in section 7 has a strong tendency to use pointer arithmetic in preference to array indices.

Pointers are not type-safe Another way in which pointers in C differ from high-level languages' references is that you're not constrained to point them at objects of the right type.

A reference in a high-level language can be relied on to either point at a valid object of the right type, or at NULL or nil or None or some such. We've already seen section 3.

Pointers are just addresses in memory, and C doesn't assume it knows better than you about what you keep where in memory. So C will typically let you just construct any pointer value you like by casting an integer to a pointer type, or by taking an existing pointer to one type and casting it so that it becomes a pointer to an entirely different type. For example, in section 2 I already mentioned that you can treat any C object of any type as a plain sequence of bytes, just by taking the address of the object and casting it to a pointer to char.

It's not generally a good idea to rely on the exact byte values you'll read out of an object that way; the exact details of objects' memory layout will vary between platforms, so you won't get the same answers on every kind of system if you do this. But you can depend on a few things, such as that if you copy a whole object byte by byte from one place to another then you'll end up with a valid copy of the same object at the destination. Arrays are not bounds-checked In higher-level languages, you're probably used to the idea that looking up an element of an array will either successfully return an element if the index is in the correct range, or else crash with an exception of some kind.

In order to do this, arrays have to come with some implicit metadata indicating their length, and the language generally lets you access that metadata directly as well len array in Python, array.

In C, arrays are a much simpler and more primitive concept. An array is just some number of pieces of data of the same type, all laid out in memory end-to-end.

You have a pointer to the start of the array, and you access array[i] by first adding i to the value of that pointer, and then looking up whatever is in memory at that location.

So the length of the array isn't stored in memory anywhere, and therefore C arrays have no way to look up the length at run time like Java and Python do. This also means that you are responsible for making sure you don't overrun the bounds of the array: Instead, overrunning an array will have effects similar to those of dereferencing a stale pointer see section 3.

C (programming language)

Therefore, it's important to make sure you keep track of array lengths yourself. This is often done by keeping the array pointer alongside a variable giving the array's length; alternatively, you might arrange that the array has some kind of recognisable terminating element at the end, and then any function to which you pass a pointer to the array must make sure to stop when it encounters that terminating element.

Strings are often handled this way; see section 7. A compensatory advantage to C's very primitive concept of arrays is that you can pretend that they're a different size or that they start in a different place.

Allocated memory must be manually freed Perhaps the best-known difference between C and high-level languages is the manual memory management. In C, things are not too different: So if you pass sizeof the wrong thing to malloc, nothing at compile time will warn you that you've allocated the wrong amount of memory. This is another way in which you can accidentally overwrite important data when programming in C.

The difference in C is that when you've finished with that piece of memory, you have to dispose of it by hand, by calling the function free and passing it the same address you got from malloc. This has two complementary consequences. Firstly, of course, it means you have to remember to free your memory, and in particular, to free it at the right moment — after it's not needed any more, but before you lose all your copies of the pointer so that you wouldn't be able to free it anyway.

And secondly, this gives you another way in which pointers can become stale: In particular, you mustn't free a pointer that's already been freed. Freeing twice is an error and will typically corrupt the memory allocator's state.

The owner of the memory is the only one who can free it. So the piece of code which owns the pointer must make sure to free it at some appropriate moment e. So you need to think about how that's going to work, and find a way for non-owners of the pointer to avoid making that mistake.

There are lots of ways to do that.

the existing relationship between c and language

For example, you might be able to arrange that the owner is freed last, so that all the non-owners have gone away already before the owner calls free. Alternatively, you might keep a list of non-owners, and notify them all when you free the memory. Undefined behaviour In previous sections I've described a number of things you can get wrong in a C program — accessing stale pointers, allocating the wrong size of memory, overrunning the bounds of an array, freeing the same pointer twice — which will cause your program to overwrite the wrong piece of memory.

In C, you are not protected in either of those ways, so making mistakes of this kind can lead to your program corrupting pieces of memory that other parts of the program were depending on. If you're lucky, this will lead to a reasonably prompt crash of some kind; but if you're unlucky, the effects won't be immediately noticeable, and your program will appear to work sensibly for the moment and then fail much later for no obvious reason. Worse still, if your program is on a security boundary and any of these errors can occur in response to input from untrusted users, then a malicious attacker may be able to manipulate errors like this to arrange to overwrite particular pieces of memory on purpose, and perhaps take control of your program.

What are the differences between C, C# and C++ in terms of real-world application - Stack Overflow

The C standard is intentionally only a partial specification of how programs must behave: Overwriting the wrong piece of memory is a major and important example of undefined behaviour, but it's not the only one.

There are other things which you should avoid doing in C, but which the language implementation won't give you any help with, and if you do get them wrong then unpredictable weirdness can result. An example of this is integer overflow: You could imagine several plausible things that might happen if you try this: In fact, C says that the behaviour if you do this is completely undefined: For example, consider this code: We first make sure n is positive; then even after we add to it, we check again that it's positive, in case wraparound due to integer overflow caused it to become negative.

You could imagine the function crashing, if it were compiled and run on a platform where that's the response to overflow, but if it returns at all then surely it must return either zero, or a positive integer. Because the compiler knows after the first if statement that n is positive, and then it assumes that integer overflow does not occur and uses that assumption to conclude that the value of n after the addition must still be positive, so it completely removes the second if statement and returns the result of the addition unchecked.

Put another way, you could imagine that the compiler is thinking to itself: So they must be implicitly promising to always call this function with input values that don't cause overflow — in which case the function doesn't need the second test, and will run faster with it removed.

It's just that the test you deliberately put in as a safety check hasn't worked, because undefined behaviour is too weird for any safety check to be able to reliably spot it after it's happened.

And even that is still only one possible example of how a program might misbehave if you cause undefined behaviour — another time, it might be some other totally different thing that you couldn't have predicted in advance. The only safe thing is not to allow undefined behaviour to happen in the first place: There is no convenient string type String handling in C is very, very primitive by the standards of almost any other language.

In Java or Python, you expect that most of the time you can treat string variables just like any other kind of variable. In C, that's not true at all. That is to say, you just have a lot of chars laid end-to-end in memory. The standard convention although you can choose to do it differently if you need to is that strings are terminated with a zero byte; so if you pass a string to a function, for example, you typically just pass a char pointer that points to the first character of the string, and the function receiving it has to search along the string for the zero byte if it wants to know how long the string is.

C (programming language) - Wikipedia

The interesting effect of this is: Where do you put it? You need to find an appropriately sized chunk of memory to keep your new string in. The most obvious approach is to use malloc to allocate a chunk of memory the right size.

In order to do that, first you have to find out the lengths of your two input strings, by counting along each one looking for the terminating zero byte. Pointers can be manipulated using assignment or pointer arithmetic. The run-time representation of a pointer value is typically a raw memory address perhaps augmented by an offset-within-word fieldbut since a pointer's type includes the type of the thing pointed to, expressions including pointers can be type-checked at compile time.

Pointer arithmetic is automatically scaled by the size of the pointed-to data type.

the existing relationship between c and language

Pointers are used for many purposes in C. Text strings are commonly manipulated using pointers into arrays of characters. Dynamic memory allocation is performed using pointers. Many data types, such as treesare commonly implemented as dynamically allocated struct objects linked together using pointers.

Pointers to functions are useful for passing functions as arguments to higher-order functions such as qsort or bsearch or as callbacks to be invoked by event handlers. Dereferencing a null pointer value is undefined, often resulting in a segmentation fault.

Null pointer values are useful for indicating special cases such as no "next" pointer in the final node of a linked listor as an error indication from functions returning pointers. In appropriate contexts in source code, such as for assigning to a pointer variable, a null pointer constant can be written as 0, with or without explicit casting to a pointer type, or as the NULL macro defined by several standard headers.

In conditional contexts, null pointer values evaluate to false, while all other pointer values evaluate to true. Since the size and type of the pointed-to object is not known, void pointers cannot be dereferenced, nor is pointer arithmetic on them allowed, although they can easily be and in many contexts implicitly are converted to and from any other object pointer type. Because they are typically unchecked, a pointer variable can be made to point to any arbitrary location, which can cause undesirable effects.

Although properly used pointers point to safe places, they can be made to point to unsafe places by using invalid pointer arithmetic ; the objects they point to may continue to be used after deallocation dangling pointers ; they may be used without having been initialized wild pointers ; or they may be directly assigned an unsafe value using a cast, union, or through another corrupt pointer.

In general, C is permissive in allowing manipulation of and conversion between pointer types, although compilers typically provide options for various levels of checking. Some other programming languages address these problems by using more restrictive reference types. C string Array types in C are traditionally of a fixed, static size specified at compile time. The more recent C99 standard also allows a form of variable-length arrays.

However, it is also possible to allocate a block of memory of arbitrary size at run-time, using the standard library's malloc function, and treat it as an array. C's unification of arrays and pointers means that declared arrays and these dynamically allocated simulated arrays are virtually interchangeable. Since arrays are always accessed in effect via pointers, array accesses are typically not checked against the underlying array size, although some compilers may provide bounds checking as an option.

If bounds checking is desired, it must be done manually. C does not have a special provision for declaring multi-dimensional arraysbut rather relies on recursion within the type system to declare arrays of arrays, which effectively accomplishes the same thing. The index values of the resulting "multi-dimensional array" can be thought of as increasing in row-major order. The pool of people using it is smaller, making it a less desirable target for hackers. It was created by a Ph.

His goal was to enhance C and add object-oriented programming capabilities without sacrificing speed or efficiency. It was developed by a team at Microsoft lead by Anders Hejlsberg in NET framework, but its backbone is still clearly the C language.

C compiles into byte-code, rather than machine code. That means it executes on a virtual computer that translates it into machine code on the fly. It adds garbage collection, uninitialized variable checking, bound checking, and type checking capabilities to the base C code. C typically sees use in internal or enterprise applications, rather than commercial software. Con the other hand, has more in common with languages like Java. Photo credit to Codecondo C vs. The term object-oriented, as it relates to programming, originated at MIT in the late 50s or early 60s.

A class can be made up of data or code procedures also known as methods.