I have one requirement in C.
char abc[]="hello";
char hello[]="world";
Using abc whether we can get the hello variable's value in C. I know it is possible in some of the languages like Perl, Php, Bash,.,
Is it possible in C?
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3What do you mean by "get the hello variable's value" ?Paul R– Paul R2010-03-05 12:19:47 +00:00Commented Mar 5, 2010 at 12:19
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1He intends to do something like ( abc[] )[]. This is possible in PHP, not in C. C is not dynamic!N 1.1– N 1.12010-03-05 12:20:45 +00:00Commented Mar 5, 2010 at 12:20
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2He means using name of the variable as string to obtain its value.zweihander– zweihander2010-03-05 12:20:46 +00:00Commented Mar 5, 2010 at 12:20
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I think you're going to have to re-word this question to make it clearer. Maybe you could provide an example in Perl or Bash so that we could see what you mean?Douglas Leeder– Douglas Leeder2010-03-05 12:22:05 +00:00Commented Mar 5, 2010 at 12:22
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6 Answers
Yes you are right , this is possible in some other language but not in C , since abc is a container which resides in a location (for ex: 1000) and hello is one more container which resides in another location ( for ex : 2000 ) , so we have no contact between these two arrays ,
we cannot make a value ( strings ) to point some other value. so finally THIS IS NOT AT ALL POSSIBLE.
answered Mar 5, 2010 at 12:25
Abubacker Nainamohamed
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No, this is not possible in C without providing a string lookup table of some sort that could link variables with their names.
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It's impossible in C, unlike in more dynamic languages like Perl or Python. However, it's important to keep in mind that even in those languages this isn't recommended. I haven't seen a snippet of code putting this to a good use yet. The eval methods available in dynamic languages are used sparingly, and not for dynamically grabbing variable names.
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As soon as the C compiler has figured out where to store the underlying pointers, it forgets about the name you gave it. The dynamic languages solve it with a data structure like a hash map which allows you to store the pointers (value) under a key (the name).
Another option is to read in the debug information. This is only available if you compile your code with -g (gcc) or some other, compiler specific option. Note that the debug format is not standardized, so you'll need to figure out what your compiler uses and how to work with it.
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It is not possible in C. It can be done in java by reflection in some cases.
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POSIX has several functions that allows you to do it, assuming variable hello is global and isn't static:
void *handle = dlopen(NULL, RTLD_NOW);
// error handling omitted
printf("%s variable contains value %s", abc, (char *)dlsym(handle, abc));
dlsym() return value is casted to char * to suppress warning when using compilers that check format string for printf-alike functions.
And you need to make sure you've specified correct compiler options, e.g. -rdynamic -ldl in case of GCC.
