Get the maximum value of a variable in C

Question

Is there a function in C that returns the maximum value of a variable like this (I will name the function \"maxvalue\" in example below)?

int a;
printf(\"%d\", m         


        

Answer 1

Here are macros from my library that work for types, rather than variables:

/* min and max integer values.  T is a signed or unsigned integer type. */

/* Returns 1 if T is signed, else 0. */
#define INTTYPE_SIGNED(T) ((T)-1 < (T)0)

/*
 * Returns (T)(maximum value of a T).
 *
 * Pains are taken (perhaps unnecessarily) to avoid integer overflow
 * with signed types.
 */
#define INTTYPE_MAX(T)                      \
    (((T)1 << (CHAR_BIT*sizeof(T)-INTTYPE_SIGNED(T)-1)) - 1 +   \
     ((T)1 << (CHAR_BIT*sizeof(T)-INTTYPE_SIGNED(T)-1)))

/*
 * Returns (T)(minimum value of a T).

 * Pains are taken (perhaps unnecessarily) to avoid integer overflow
 * with signed types.
 * assert: twos complement architecture
 */
#define INTTYPE_MIN(T) ((T)(-INTTYPE_MAX(T)-1))

Edit: Adapting these to the question:

/* min and max integer values.  V is a signed or unsigned integer value. */

/* Returns 1 if V has signed type, else 0. */
#define INT_VALUE_SIGNED(V) ((V)-(V)-1 < 0)

/*
 * Returns maximum value for V's type.
 *
 * Pains are taken (perhaps unnecessarily) to avoid integer overflow
 * with signed types.
 */
#define INT_VALUE_MAX(V)                        \
    (((V)-(V)+1 << (CHAR_BIT*sizeof(V)-INT_VALUE_SIGNED(V)-1)) - 1 +    \
     ((V)-(V)+1 << (CHAR_BIT*sizeof(V)-INT_VALUE_SIGNED(V)-1)))

/*
 * Returns minimum value for V's type.

 * Pains are taken (perhaps unnecessarily) to avoid integer overflow
 * with signed types.
 * assert: twos complement architecture
 */
#define INT_VALUE_MIN(V) (-INT_VALUE_MAX(V)-1)

Afterthought: These invoke UB if V is a variable, or an expression containing variables, that have not been assigned a value ... which is the case in the question as asked. They are likely to work on many implementations, but the C standard doesn't guarantee it, and they will certainly fail on an implementation that initializes uninitialized variables with trap values.