The equivalent python exec/eval commands in C

Question

is there a exec() / eval() function in C??

for example..

exec(printf(3 + 4))

or

eval(printf(3 + 4))

i've done this in python... but i don't know how to do this in C and C languages..

i understand that this might be harmful in python as it can take any input.. so to overcome that i came to C which is more strict

this is just a experiment i am curious to learn

an explaination would be appreiciated

i am using sublime text (just in case...:] )

No `C` standard doesn't support any such functions. `C` is strictly typed language. — kiran Biradar, Jun 05 '20 at 08:39
No, there is not a built-in function like that. See discussion of why here: https://www.quora.com/What-is-a-method-in-C++-to-evaluate-strings-like-eval-in-Python#:~:text=C%2B%2B%20programs%20can%20run%20on,but%20it's%20a%20bit%20tricky. There are weird ways to do something similar, but they are slow and not worth the trouble: https://stackoverflow.com/questions/39091681/writing-eval-in-c — jdaz, Jun 05 '20 at 08:40
I am not sure tha C have this built in functions like. In C language, if you wish to `execute` some code you need to `fork()` and `execv` (family of executions) or to execute function by spawning a `thread` and let him do the job. Or to `load` dynamic library, `SO` — Adam, Jun 05 '20 at 08:41
Adam do you have a link / example to use fork() and execv ()? — CodeMaster, Jun 05 '20 at 08:51
i don't know how to spawn thread , load either.... kind of a begginer in c.. — CodeMaster, Jun 05 '20 at 08:53

alinsoar · Accepted Answer · 2020-06-05T12:01:24.707

1

Python is a simplified Lisp and in Lisp there is the eval/apply paradigm. In C this paradigm exists only inside the compiler. The compilation system of C uses eval/apply, also called the Maxwell equations of software. But at user level you do not interact with eval/apply, only if you write/develop in C a compiler for a language you cope with.

So in C you need to implement this yourself, in case you develop some language that is Turing complete (a Turing machine is equivalent with eval+apply cycle).

edited Jun 05 '20 at 12:01

answered Jun 05 '20 at 08:51

alinsoar

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Interesting reference, "Maxwell equations of software" – Paul Ogilvie Jun 05 '20 at 08:58
its going to be difficult I_I – CodeMaster Jun 05 '20 at 11:53

Paul Ogilvie · Answer 2 · 2020-06-05T08:59:53.537

An eval() function is typical of interpreter based languages. An interpreter is a "compiler on the fly" that interprets (hence its name) the program text and executes the program commands immediately.

An interpreter based language requires a program to be running that can read the program text and execute its instructions.

C is a compiler based language which means that the program text is translated "off-line" into an executable format that can run without a program to interpret the program text.

Because C does not have such an interpreter program running (and so the program does not have a language system "on board"), it has no way to interpret C program text in an eval function. For that reason, such functions do not exist in C.

The equivalent python exec/eval commands in C

2 Answers2