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Operator overloading in C
(7 answers)
How do you get assembler output from C/C++ source in GCC?
(17 answers)
Is it possible to overload operators in C?
(4 answers)
Closed 4 years ago.
Is there a way that we can call user defined function when we are calling arithmetic operator in a C program just like operator overloading in C++. using GNU GCC Compiler?
Simply,
I have a function add(), and in my C program I have arithmetic Operation
c = a + b;
when I compile the program, it should call my add() function internally for + operator.
and Is there a way we can see what is the code that gcc compiler is calling when it encounters + operator?
No.
C does not work that way, you cannot overload/override the basic built-in operators.
Seeing the code is of course possible, either by making gcc emit it directly using -S, or by disassembling the resulting binary. The related binutils tool is objdump.
These days much such exploration can also be made "online" using the fantastic Compiler Explorer tools at godbolt.org, of course.
Related
This question already has answers here:
How to get and evaluate the Expressions from a string in C
(4 answers)
How to Write a Boolean Expression Evaluator in C?
(9 answers)
Simple library or implementation for a mathematical expression evaluator [closed]
(7 answers)
Is there any C function that can evalute a string expression defined in the standard library?
(3 answers)
How to evaluate a mathematical expression using strings and arrays in C [closed]
(2 answers)
Closed 2 years ago.
I was wondering if there was a way to run code stored as a string in a variable. Ie str code = "i=5+6"
Anyone got any ideas?
The C language itself has no evaluation function as you find in many interpreted languages.
For an interpreted language, where the source code is passed to an interpreter for execution, it is very easy to later on pass a string to the same interpreter.
C is typically a compiled language, it is passed to a compiler program that translates the C code into CPU instructions that are directly executed by your CPU. The same thing would need to happen with your string content. Yet the system running a compiled C program may not even have a compiler installed as a compiler is not required to run the final program, only to create it.
To dynamically run C code, your program would need to have an entire compiler built-in or a C interpreter.
See also:
Is there an interpreter for C?
https://www.drdobbs.com/cpp/building-your-own-c-interpreter/184408184
This is nothing for a beginner, though, this is something most C experts would not even consider.
If you dynamically need to execute code at runtime, the easiest I can think of is using Lua. The Lua interpreter can be linked into your program, it's very small for a language interpreter, and you can then pass a string of Lua code to the interpreter at runtime.
https://www.lua.org/
Of course, there are even smaller interpreters for other languages (e.g. Lisp) but IMHO most programmers would not find those other languages very appealing while Lua will immediately look common to them.
This question already has answers here:
Are nested functions a bad thing in gcc ? [closed]
(11 answers)
Implementation of nested functions
(1 answer)
Nested function in C
(9 answers)
Closed 3 years ago.
I wrote a small program in C on Ubuntu having function definitions within the main function and compiled it using GCC. It compiled and ran without error. However, writing the same program in Codeblocks on Windows doesn't compile, and issues an error that says function-definition is not allowed here.
So, does GCC on Ubuntu allow function definitions within a function? Will it always run perfectly (given that it has compiled and there is no logical error in the program)?
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undefined reference to "only some math.h" functions
(4 answers)
Closed 5 years ago.
I just encountered a strange thing. While testing math.h I tried to use pow() and compile it. I did not have to link math.h .
But when I try the same with something like fmod() I have to link math.h while compiling the programm.
Why do I have to link the library in the second case but not in the first?
Your compiler may be replacing some usages of pow with a constant. For example, it could replace pow(2.0, 3.0) with 8.0. This is a good optimisation and means you no longer need the pow in math.h.
But your compiler probably can't replace fmod, or all usages of math functions, so it still needs to link to the math library.
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
How was the first compiler written?
I'm asking this as a single question because, essentially what I'm trying to ask is at the bottom how is all of this implemented, here goes:
How was the first C compiler generated, since C compiler is written in C itself then how was the first source of C compiler generated?
Is C written in ASM, how are languages actually designed?, because before we had high level languages the only way to design something was through ASM, even if C is derived from earlier languages, how were they designed? (My clue is ASM)
I'm getting confused as to how does C work down at the bottom. What I'm trying to say is since at the bottom, everything is implemented at the processor by OPcodes. So what my understanding was that C programs are "essentially" translated to Sys Calls which are implemented by the Kernel.
But then how are syscalls implemented? (Do they directly correspond to OPcodes or is there any other layer of abstraction.
How was the first C compiler generated, since C compiler is written in C itself then how was the first source of C compiler generated?
Bootstrapping.
This question already has answers here:
Closed 11 years ago.
Possible Duplicate:
Undefined Behavior and Sequence Points
Which 'C' compiler gives the logically correct answers... I mean Turbo C older version or the newer one named as Borland cpp 4.5 and above?
The different outputs of the question { int i=5;printf(i++*++i);} made me ask this.
No C compiler will give a correct answer.
The most correct answer would be to detect nonsense of this kind and refuse to compile it with an error message.