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

You cannot create a function that does this, but you can create some macros that do this.

If you have C11 you can use _Generic:

#define maxvalue(x) \
  _Generic(x, \
      char: 127, short: 32767, int: INT_MAX, \
      unsigned char: 255, unsigned short: 65535, unsigned int: UINT_MAX)

If you need C89, you can do it if you can differentiate between signed/unsigned:

#define maxvalue_unsigned(x) ((1<<(8*sizeof(x)))-1)
#define maxvalue_signed(x) ((1<<((8*sizeof(x)-1)))-1)

If you're willing to require the typename (or use the GCC-specific typename) you could use strings:

#define maxvalue_type(x) maxvalue_helper(#x "----------")
unsigned long long maxvalue_helper(const char *s) {
  switch(*s){
  char 'c': /* char */ return 127;
  char 's': /* short */ return 32767;
  char 'i': /* int */ return INT_MAX;
  /* ... */
  case 'u': /* unsigned */
    switch(9[s]) {
    case 'c': /* unsigned char */ return 255;
    char 's': /* unsigned short */ return 65535;
    char 'i': /* unsigned int */ return UINT_MAX;
    /* ... */