How many chars can be in a char array?

c arrays memory char buffer
user666010 picture user666010 · Mar 18, 2011 · Viewed 50.3k times · Source 
#define HUGE_NUMBER ???

char string[HUGE_NUMBER];
do_something_with_the_string(string);

I was wondering what would be the maximum number that I could add to a char array without risking any potential memory problems, buffer overflows or the like. I wanted to get user input into it, and possibly the maximum possible.

Answer

Greg picture Greg · Mar 18, 2011

See this response by Jack Klein (see original post):

The original C standard (ANSI 1989/ISO 1990) required that a compiler successfully translate at least one program containing at least one example of a set of environmental limits. One of those limits was being able to create an object of at least 32,767 bytes.

This minimum limit was raised in the 1999 update to the C standard to be at least 65,535 bytes.

No C implementation is required to provide for objects greater than that size, which means that they don't need to allow for an array of ints greater than (int)(65535 / sizeof(int)).

In very practical terms, on modern computers, it is not possible to say in advance how large an array can be created. It can depend on things like the amount of physical memory installed in the computer, the amount of virtual memory provided by the OS, the number of other tasks, drivers, and programs already running and how much memory that are using. So your program may be able to use more or less memory running today than it could use yesterday or it will be able to use tomorrow.

Many platforms place their strictest limits on automatic objects, that is those defined inside of a function without the use of the 'static' keyword. On some platforms you can create larger arrays if they are static or by dynamic allocation.

Now, to provide a slightly more tailored answer, DO NOT DECLARE HUGE ARRAYS TO AVOID BUFFER OVERFLOWS. That's close to the worst practice one can think of in C. Rather, spend some time writing good code, and carefully make sure that no buffer overflow will occur. Also, if you do not know the size of your array in advance, look at malloc, it might come in handy :P

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