Today as a small experiment I wrote very simple C program to display min and max values of the basic object types.
/* Display min/max limits using limits.h header file */ #include <stdio.h> /* printf */ #include <limits.h> /* limits */ #include <assert.h> /* assert */ #define COMPUTE 1 /* used values: * * 0 - do not calculate min/max values * 1 - calculate min/max values with exceptions for "long" types * 2 - calculate min/max values without any exceptions */ /* calculate max value */ #define max(var, temp) \ var=0; temp=0; \ while((++var)>0) \ temp++; /* calculate min value */ #define min(var, temp) \ var=0; temp=0; \ while((--var)<0) \ temp--; /* print description and min/max limits using limits.h */ #define describe(description, type, min, max) \ printf("%s\n\tlimits.h: <%" type ", %" type ">\n", \ description, min, max); /* calculate and print min/max values */ #define calculate(var, type, vmin, vmax) \ min(var, vmin); \ max(var, vmax); \ printf("\tcalculated: <%" type ", %" type ">\n", \ vmin, vmax); int main() { /* signed char */ describe("signed char", "hhd", SCHAR_MIN, SCHAR_MAX); # if COMPUTE signed char schar, schar_max, schar_min; calculate(schar, "hhd", schar_min, schar_max); assert(schar_min == SCHAR_MIN && schar_max == SCHAR_MAX); # endif /* unsigned char */ describe("unsigned char", "hhu", 0, UCHAR_MAX); # if COMPUTE unsigned char uchar, uchar_min, uchar_max; calculate(uchar, "hhu", uchar_min, uchar_max); assert(uchar_min == 0 && uchar_max == UCHAR_MAX); # endif /* char */ describe("char", "hhd", CHAR_MIN, CHAR_MAX); # if COMPUTE char character, char_min, char_max; calculate(character, "hhd", char_min, char_max); assert(char_min == CHAR_MIN && char_max == CHAR_MAX); # endif /* signed short int */ describe("signed short int", "hd", SHRT_MIN, SHRT_MAX); # if COMPUTE signed short int ssint, ssint_min, ssint_max; calculate(ssint, "hd", ssint_min, ssint_max); assert(ssint_min == SHRT_MIN && ssint_max == SHRT_MAX); # endif /* unsigned short int */ describe("unsigned short int", "hu", 0, USHRT_MAX); # if COMPUTE unsigned short int usint, usint_min, usint_max; calculate(usint, "hu", usint_min, usint_max); assert(usint_min == 0 && usint_max == USHRT_MAX); # endif /* signed long int */ describe("signed long int", "ld", LONG_MIN, LONG_MAX); # if COMPUTE == 2 signed long int slint, slint_min, slint_max; calculate(slint, "ld", slint_min, slint_max); assert(slint_min == LONG_MIN && slint_max == LONG_MAX); # endif /* unsigned long int */ describe("unsigned long int", "lu", (unsigned long int) 0, ULONG_MAX); # if COMPUTE == 2 unsigned long int ulint, ulint_min, ulint_max; calculate(ulint, "lu", ulint_min, ulint_max); assert(ulint_min == 0 && ulint_max == ULONG_MAX); # endif #if defined __USE_ISOC99 && defined __GNUC__ /* signed long long int */ describe("signed long long int", "lld", LLONG_MIN, LLONG_MAX); # if COMPUTE == 2 signed long long int sllint, sllint_min, sllint_max; calculate(sllint, "lld", sllint_min, sllint_max); assert(sllint_min == LLONG_MIN && sllint_max == LLONG_MAX); # endif /* unsigned long long int */ describe("unsigned long long int", "llu", \ (unsigned long long int) 0, ULLONG_MAX); # if COMPUTE == 2 unsigned long long int ullint, ullint_min, ullint_max; calculate(ullint, "llu", ullint_min, ullint_max); assert(ullint_min == 0 && ullint_max == ULLONG_MAX); # endif #endif /* signed int */ describe("signed int", "d", INT_MIN, INT_MAX); # if COMPUTE signed int sint, sint_min, sint_max; calculate(sint, "d", sint_min, sint_max); assert(sint_min == INT_MIN && sint_max == INT_MAX); # endif /* unsigned int */ describe("unsigned int", "u", 0, UINT_MAX); # if COMPUTE unsigned int uint, uint_min, uint_max; calculate(uint, "u", uint_min, uint_max); assert(uint_min == 0 && uint_max == UINT_MAX); # endif return 0; } |
Sample output:
$ gcc limits.c -o limits $ ./limits signed char limits.h: <-128, 127> unsigned char limits.h: <0, 255> char limits.h: <-128, 127> signed short int limits.h: <-32768, 32767> unsigned short int limits.h: <0, 65535> signed long int limits.h: <-9223372036854775808, 9223372036854775807> unsigned long int limits.h: <0, 18446744073709551615> signed long long int limits.h: <-9223372036854775808, 9223372036854775807> unsigned long long int limits.h: <0, 18446744073709551615> signed int limits.h: <-2147483648, 2147483647> unsigned int limits.h: <0, 4294967295> |
Sample output (ISO C90 standard):
$ gcc -std=c89 limits.c -o limits $ ./limits signed char limits.h: <-128, 127> unsigned char limits.h: <0, 255> char limits.h: <-128, 127> signed short int limits.h: <-32768, 32767> unsigned short int limits.h: <0, 65535> signed long int limits.h: <-9223372036854775808, 9223372036854775807> unsigned long int limits.h: <0, 18446744073709551615> signed int limits.h: <-2147483648, 2147483647> unsigned int limits.h: <0, 4294967295> |
To calculate min and max values modify the COMPUTE constant in the source code.
$ gcc limits.c -o limits $ ./limits signed char limits.h: <-128, 127> calculated: <-128, 127> unsigned char limits.h: <0, 255> calculated: <0, 255> char limits.h: <-128, 127> calculated: <-128, 127> signed short int limits.h: <-32768, 32767> calculated: <-32768, 32767> unsigned short int limits.h: <0, 65535> calculated: <0, 65535> signed long int limits.h: <-9223372036854775808, 9223372036854775807> unsigned long int limits.h: <0, 18446744073709551615> signed long long int limits.h: <-9223372036854775808, 9223372036854775807> unsigned long long int limits.h: <0, 18446744073709551615> signed int limits.h: <-2147483648, 2147483647> calculated: <-2147483648, 2147483647> unsigned int limits.h: <0, 4294967295> calculated: <0, 4294967295> |
If you want to use gcc optimization flags then read about -fno-strict-overflow-fwrapv
$ gcc -Os -fwrapv limits.c -o limits |