Will - No. Languages aren't fast, only their implementations. Language implemtations can be fast or slow in a variety of areas and testing all of them is undoubtedly impossible. A better question would be "Why do language designers choose X language instead of Y language? Show 13 more comments. Active Oldest Votes. Improve this answer. Potatoswatter Potatoswatter k 22 22 gold badges silver badges bronze badges.
Too bad In fact, a typical size-conscious embedded SQLITE application has a fixed query set, and the database is memory-mapped from flash, with fixed schema, and the SQL interpreter and VM are dead weight, as is a lot of other code. UnslanderMonica 1. SQLite is bytecode-based. That suggests architectural changes such that the product wouldn't be SQLite any more. Show 1 more comment.
EDIT: On the interoperability side The std::sort is one such example: the std::less functor used by default is not less efficient than the equivalent C function, but all compilers I know will inline it being a template it is available for inlining and remove all of the function calls to the compare functor.
Who knows how well that reasoning holds up nowadays. Add a comment. Scripted languages are inheritantly slower then compiled ones, unless you write truly awful compiled code — Will03uk.
Will03uk - What keeps you from writing a compiler for a usually scripted language? In the present times, software design includes the combination of both approaches to get the best of both worlds. However, no such feature is offered by the C programming language.
As data and functions are treated as distinct entities in the C programming language, there is no support for encapsulation. In the C programming language, data not as secure. Modifiers can be used for class members in order to make the data inaccessible for external users.
No such concept exists in the C programming language. As a consequence, all variables are open and therefore, vulnerable to be accessed by some malicious code. Declaring enumerations are possible in C. However, the declared enumeration constants are of integer type.
In that sense, an enumeration declaration is similar to declaring a number of integer constants. Plus, there is no additional type safety. Nonetheless, it is possible to assign a value of an enumeration type to some variable of the integer type. This is because enumeration types allow implicit conversion by means of integral promotion.
A static checker can easily detect this implicit conversion and provide a warning if needed. The char[] represents string literals in C. When passed to some external function, there is a good possibility of the function modifying the original string. To make things even worse, there is no way to prevent such a happening.
C supports inbuilt and primitive data types. No such inbuilt data types exist in the C programming language. While C uses stdio. C is described as a hands-on programming language. Hence, it is essential to tell the program everything that needs to be done. Conventionally, a programmer coding in C needs to prevent errors from occurring beforehand. Hence, it is required to test return values from functions.
In the worst case where the error is inevitable, the programmer must log the error and terminate the program gracefully. Any C program is saved with a. It enables a function with the same name to be defined for varying purposes. Overloaded functions have the same name albeit different parameters.
For instance, a function add can be defined in two ways. While one is able to calculate the sum of integer values, the other version can concatenate two or more strings. If such a function is called by passing argument s then those argument s are used by the function.
Inheritance is the ability of a class to derive properties as well as characteristics from some other class. As it is one of the important properties of OOPS, no such feature is available in the C programming language.
The class that inherits properties from another class is called the child class. It might also be known as derived or subclass.
The class whose properties are inherited by the subclass is known as the base class. It is also referred to as the parent or superclass. C makes use of the Macro function as a means for optimization technique, especially for reducing the overall execution time.
Functions that are instructed as inline functions to the compiler allows it to replace their function definition wherever they are being called. If the function is too big then the compiler can ignore the inline request and execute them as normal functions. The C programming language uses scanf and printf for input and output, in the respective order, operations. The C programming language has a very complicated mapping between data and function. C offers calloc and malloc functions for dynamic memory allocation and the free function for memory deallocation.
Namespaces grant the ability to group named entities into a narrower scope, called the namespace scope. Without namespaces, these named entities would have a global scope. In other words, a namespace is a declarative region providing a scope to the identifiers inside it. The simple reason for using namespaces is to organize the elements of the program into distinct logical scopes referred to by names.
All declarations made within such blocks are declared in the named scope. Any namespace definition starts with the namespace keyword followed by the name of the namespace.
The general syntax is:. Simply, it is a feature that allows changing the way an operator works for user-defined types. In fact, C says that the behaviour if you do this is completely undefined: that is, any of those reasonably sensible things could happen, but anything else could happen instead, no matter how silly.
For example, consider this code:. Looking at this function, you'd think there was no way it could return a negative number. 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.
Actually, no. 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. 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.
So beware! The only safe thing is not to allow undefined behaviour to happen in the first place: for example, in the above code, the right thing would have been to check whether n is close to overflow before trying to add anything to it, and not do the addition at all if so. 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 char s 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.
The interesting effect of this is: suppose you want to construct a new string, for example by concatenating two existing strings. 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.
Then you have to call malloc and ask for a number of bytes equal to the sum of those two lengths plus one leaving room for the terminating zero byte , and then you have to copy the actual string data from the two input strings into the newly allocated memory.
And then , of course, you have to keep track of when you've finished with the string, and remember to free it once it's no longer needed. And it's a typical example, unfortunately: most string handling operations in C are about as annoying as that. Of course, the comparatively easy string handling in high-level languages will really be having to do all of this same work; it's just that the language hides it from you, and takes care of the tedious details automatically. So in a high-level language, you can easily write some pretty slow string-handling code without really noticing — you can concatenate two strings with a single plus sign, and in some situations that one character can cause the language to have to move megabytes of data bodily around the computer's memory.
In C, you're much more likely to notice that the string handling you asked for is likely to be long and tedious and slow — and sometimes, you can find ways to avoid some of the pain. For example, suppose you've got a long string, and you want to break it up at the space characters so that you end up with lots of smaller strings representing individual words. If you do that in a high-level language with the built-in string handling, you'll almost certainly end up with a series of string variables containing copies of the parts of the original string that contain each word.
In C, a common approach to this problem at least if you didn't need the original string itself afterwards, which you often don't avoids having to actually copy anything , so it will run much faster. What you do is to modify the original array of char s, by writing zero bytes just beyond the ends of words. For example, suppose you have an input string like this:. Now we can construct an array of char -pointer values let's call it ptrs pointing at the beginning of each word.
For example, our pointer array might look like this in memory So each pointer points to a zero-terminated string containing one of the original words. Hence, we've effectively constructed a separate string value per word, without ever having to move the string data from one place to another or allocate new memory to contain copies of it.
Well, we probably did have to allocate memory for our ptrs array, but that's typically a lot smaller. In C, this kind of trickery is done as often as possible, to save the considerable pain of allocating memory and copying stuff. When it's possible, it can make C's string handling a lot faster than doing the same thing in a high-level language — so there at least is some kind of advantage in return for all the extra programmer effort.
Something worth remembering about string handling in C is that although the standard library provides you with a set of functions to do typical things e. It can often be worth thinking about how the library function will work, and noticing that in some situations there's a way to avoid doing unnecessary work. This doesn't work as I describe above allocating new memory to put the combined string in , but instead it expects you to have spare space after the end of the first string.
So, suppose you have an enormous buffer already allocated, and you want to concatenate hundreds of little strings together. You might naturally suppose that the best way to do that is to start with an empty string and to repeatedly call strcat to add another little bit on to the end of it. But in fact, that's a slow way to do the job: each time you call strcat , it has to start at the beginning of the combined string because that's the only thing you gave it a pointer to , count all the way along it to find the zero byte at the end, and then when it finds it, write the new string into the buffer.
So if you combine lots of tiny strings this way, you'll spend most of your time walking repeatedly along the finished part. A better approach is to keep a pointer to the end of the string, i. Every time you add an extra little bit to the string, you just copy it to where your pointer currently points, and then you advance the pointer until it finds the new terminating zero.
Then you don't have to keep retracing your steps. So the string-concatenation function provided by the standard library is not always the best way to concatenate strings. Of course, in this scenario, you also have to make sure you don't overrun your buffer, either by tracking how much space you have left and stopping if you're about to go over, or by counting up the total length of all the strings in the first place and allocating the right amount beforehand.
Object orientation is pretty standard these days: most modern languages have it in some form. C does not, because it predates that being true. One very common pattern in C is just to do the same thing unofficially. That will prevent other parts of the program from reading the fields of the structure in practice, because they don't have access to the information about what the fields all are and where they live in the structure. Of course, this being C, it's possible to do uncontrolled writes to the structure regardless just convert the structure pointer into some other kind of pointer and then write into the memory it points at , but sensible programmers won't do that, because the results will almost certainly not be useful.
All of that works fine as long as you don't want to use inheritance, or Java-style interfaces, or polymorphism. In that situation, you would typically do something in C which mimics the underlying mechanism by which high-level languages implement that kind of feature: you'd define your structure type to contain some pointers to functions , and implement certain class operations by extracting one of those pointers from the structure and calling the function it points to.
That way, different instances of the same structure type could behave differently, by having their function pointer fields point at different functions.
In other words, you can do anything in C that a higher-level language's object orientation system provides. You just have to do it by hand, rather than having it done automatically for you. More importantly, you don't get the error checking. In a high-level language, you can typically take a reference to a derived class and treat it as if it was a reference to the base class, but if you try to do the same with a class that isn't a derived class of that base, you'll get a compiler error to let you know you've made a mistake.
So you can't make it diagnose only the conversions that are semantically wrong; instead, you have to use a lot of self-discipline to make sure you don't make those mistakes in the first place.
This is usually used as part of C's system for breaking a program up into modules: in order to refer to a function or variable in another module, the compiler needs to know what type the variable is, or what types of arguments and return values the function expects.
Typically you don't include a file containing the actual definitions of functions; instead, you include a file that just gives that information on its own. That declares the function, meaning that it lets the compiler know that a function with that name exists and that it takes two arguments of particular types and returns an int , but it does not define the function meaning to provide the actual code showing what the function does.
Then, in foo.
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