Limit on the number of arguments to main in C

Question

Is there a limit on the number of arguments that we pass to main() in C? As you all know, it is defined as int main(int argc, char *argv[]).

When I call the program, I can pass arguments like so:

$ prog.exe arg1 arg2 arg3.....argn

Is there an upper bound in the number of argument that we may supply to main() in this way?

Answer 1

No, there is no limit imposed by the ISO C99 standard. If you're using the "blessed" main form (of which there are two):

int main (int argc, char *argv[]);

then you will be limited to the maximum size of a signed integer (implementation-dependent but guaranteed to be at least 2¹⁵-1 or 32,767).

Of course, you could even have more than that since the standard specifically allows for non-blessed main forms (for example, one that takes a long as the count).

The standard mandates how the arguments are stored and things like argv[argc] having to be NULL, but it does not directly limit the quantity.

Of course, there will be a limit in practice but this will depend entirely on the implementation and environment. However, if you have to ask, then you're probably doing something wrong.

Most tools would place a truly large number of arguments into a response file (say args.txt) then pass a single argument like:

my_prog @args.txt

which gets around arbitrary limits on argument quantity and size.

Answer 2

According to the POSIX spec for exec, there is a macro ARG_MAX defined in <limits.h> which defines the maximum number of bytes for the arguments + environment variables.

But since C doesn't define anything about that, no, there isn't an inherent cross-platform limit. You have to consult your OS manual if it doesn't define that macro.

Answer 3

I wouldn't think so. While there may not be a theoretical limit, the computer probably can't handle 1.5 million arguments. Is there any particular reason you need to know this? I wouldn't recommend using command line arguments for thing other than options, file parameters, ect...

Answer 4

There is no limit explicit in C itself. This is an example of a behavior not defined in the language but rather the implementation. Remember that the language itself is different than it's implementation, subsequent libraries, IDE's, etc.