How to check if a variable has been initialized in C?

Question

Is there a way to check if a variable has been initialized or not in C?

Consider the following example,

int main(){     int a = 3, b = 7, c;      if ( a > b )         c = a-b;      // Now, how can I check if the variable "c" has some value or not     // I don't want check like this,     // if ( isalpha(c) ) or if ( isdigit(c) )     // or anything similar to like that } 

In other words, does C has some function like defined in Perl. In Perl, I can simply do if (defined c)that would check if the variable is defined or not, and it'd return False for above example. How can I achieve the same in C?

Answer 1

C does not have this ability. You have two main options:

A sentinel value

For example, if you know that the value of c will never be negative, then initialize it to -1, and test that for that.

Add another variable

Create another variable bool we_set_c_to_something = false; and then set it to true when you write to c.

Answer 2

C is a compiled language which doesn't support runtime variable binding, while Perl is a interpreted language which support dynamic typing. So you can check the definition of a variable in Perl, but not in C.

When you declare a variable in C int c;, this variable c is defined but without initialization. The declaration and definition are in one statement.

The definition of a variable in C is not checked by code writer. The compilers do it for you. When compile and link your C code, the compiler will check all variable's definitions. An error will be invoked and the compiling or linking process will stop if there are undefined variables found in your code.

Hope this will make you distinguish the differences.