Prints the number of bits used by, and the number of bytes allocated for, the standard types, or "-1" if unknown

type-widths.c

#include <stdio.h>
#include <limits.h>
#include <stdint.h>     // for PTRDIFF_WIDTH
#include <stdbool.h>    // for pre-C23
#include <float.h>
#include <math.h>
#include <uchar.h>

#if !defined (BOOL_WIDTH)
    #define BOOL_WIDTH (-1)
#endif
#if !defined (CHAR_WIDTH)
    #define CHAR_WIDTH (CHAR_BIT)
#endif
#if !defined (SHRT_WIDTH)
    #define SHRT_WIDTH (-1)
#endif
#if !defined (INT_WIDTH)
    #define INT_WIDTH (-1)
#endif
#if !defined (LONG_WIDTH)
    #define LONG_WIDTH (-1)
#endif
#if !defined (LLONG_WIDTH)
    #define LLONG_WIDTH (-1)
#endif
#if !defined (UINTPTR_WIDTH)
    #define UINTPTR_WIDTH (-1)
#endif

_Float16 bar();
_Float16 baz();

int main() {
    printf("            %-10s%-10s\n", "Bits", "Bytes");
    printf("%-12s%-10s%-10s\n", "Type", "Used", "Allocated");
    printf("--------------------------------\n");

    printf("%-12s%3d       %2zu\n", "bool", BOOL_WIDTH, sizeof(bool));
    printf("%-12s%3d       %2zu\n", "char", CHAR_WIDTH, sizeof(char));
    printf("%-12s%3d       %2zu\n", "short", SHRT_WIDTH, sizeof(short));
    printf("%-12s%3d       %2zu\n", "int", INT_WIDTH, sizeof(int));
    printf("%-12s%3d       %2zu\n", "long", LONG_WIDTH, sizeof(long));
    printf("%-12s%3d       %2zu\n", "long long", LLONG_WIDTH, sizeof(long long));
    printf("%-12s%3d       %2zu\n", "void *", UINTPTR_WIDTH, sizeof(void *));

    // float and double don't encode the implicit leading 0/1, but it is counted in xxx_MANT_DIG
    // log2(2 * FLT_MAX_EXP) gets us the number of bits for the exponent
    // add 1 for the sign bit
    printf("%-12s%3d       %2zu\n", "float", (FLT_MANT_DIG - 1) + (int)log2(2 * FLT_MAX_EXP) + 1, sizeof(float));
    printf("%-12s%3d       %2zu\n", "double", (DBL_MANT_DIG - 1) + (int)log2(2 * DBL_MAX_EXP) + 1, sizeof(double));
    #if defined (__x86_64__) || defined (_M_X64) || defined (i386) || defined (__i386__) || defined (__i386) || defined (_M_IX86) || defined (_X86_)
        // x87 long double *does* encode the explicit leading 0/1
        printf("%-12s%3d       %2zu\n", "long double", (LDBL_MANT_DIG) + (int)log2(2 * LDBL_MAX_EXP) + 1, sizeof(long double));
    #else
        printf("%-12s%3d       %2zu\n", "long double", (LDBL_MANT_DIG - 1) + (int)log2(2 * LDBL_MAX_EXP) + 1, sizeof(long double));
    #endif
    // these are C23-specific
    // printf("%-12s%3d       %2zu\n", "_Float16", -1, sizeof(_Float16));
    // printf("%-12s%3d       %2zu\n", "_Float128", -1, sizeof(_Float128));
}