8 <float.h> Giới hạn Dấu chấm động

#include <stdio.h>
#include <float.h>

int main(void)
{
    float pi = 3.1415926535897932384626433832795028841971;

    // Với %g hoặc %G, precision chỉ số chữ số có nghĩa:

    printf("%.*g\n", FLT_DIG, pi);  // Với tôi: 3.14159

    // Nhưng %f in quá nhiều, vì precision là số chữ số bên phải
    // dấu thập phân--nó không đếm các chữ số bên trái:

    printf("%.*f\n", FLT_DIG, pi);  // Với tôi: 3.14159... 3 ???
}

#include <stdio.h>
#include <math.h>
#include <assert.h>
#include <float.h>

int main(void)
{
    printf("FLT_DIG = %d\n", FLT_DIG);
    printf("FLT_DECIMAL_DIG = %d\n\n", FLT_DECIMAL_DIG);

    assert(FLT_DIG == 6);  // Code dưới giả định điều này

    for (float x = 0.123456; x < 0.12346; x += 0.000001) {
        printf("As written: %.*g\n", FLT_DIG, x);
        printf("As stored:  %.*g\n\n", FLT_DECIMAL_DIG, x);
    }
}

FLT_DIG = 6
FLT_DECIMAL_DIG = 9

As written: 0.123456
As stored:  0.123456001

As written: 0.123457
As stored:  0.123457

As written: 0.123458
As stored:  0.123457998

As written: 0.123459
As stored:  0.123458996

As written: 0.12346
As stored:  0.123459995

#include <stdio.h>
#include <float.h>

int main(void)
{
    printf("FLT_RADIX: %d\n", FLT_RADIX);
    printf("FLT_ROUNDS: %d\n", FLT_ROUNDS);
    printf("FLT_EVAL_METHOD: %d\n", FLT_EVAL_METHOD);
    printf("DECIMAL_DIG: %d\n\n", DECIMAL_DIG);

    printf("FLT_HAS_SUBNORM: %d\n", FLT_HAS_SUBNORM);
    printf("FLT_MANT_DIG: %d\n", FLT_MANT_DIG);
    printf("FLT_DECIMAL_DIG: %d\n", FLT_DECIMAL_DIG);
    printf("FLT_DIG: %d\n", FLT_DIG);
    printf("FLT_MIN_EXP: %d\n", FLT_MIN_EXP);
    printf("FLT_MIN_10_EXP: %d\n", FLT_MIN_10_EXP);
    printf("FLT_MAX_EXP: %d\n", FLT_MAX_EXP);
    printf("FLT_MAX_10_EXP: %d\n", FLT_MAX_10_EXP);
    printf("FLT_MIN: %.*e\n", FLT_DECIMAL_DIG, FLT_MIN);
    printf("FLT_MAX: %.*e\n", FLT_DECIMAL_DIG, FLT_MAX);
    printf("FLT_EPSILON: %.*e\n", FLT_DECIMAL_DIG, FLT_EPSILON);
    printf("FLT_TRUE_MIN: %.*e\n\n", FLT_DECIMAL_DIG, FLT_TRUE_MIN);

    printf("DBL_HAS_SUBNORM: %d\n", DBL_HAS_SUBNORM);
    printf("DBL_MANT_DIG: %d\n", DBL_MANT_DIG);
    printf("DBL_DECIMAL_DIG: %d\n", DBL_DECIMAL_DIG);
    printf("DBL_DIG: %d\n", DBL_DIG);
    printf("DBL_MIN_EXP: %d\n", DBL_MIN_EXP);
    printf("DBL_MIN_10_EXP: %d\n", DBL_MIN_10_EXP);
    printf("DBL_MAX_EXP: %d\n", DBL_MAX_EXP);
    printf("DBL_MAX_10_EXP: %d\n", DBL_MAX_10_EXP);
    printf("DBL_MIN: %.*e\n", DBL_DECIMAL_DIG, DBL_MIN);
    printf("DBL_MAX: %.*e\n", DBL_DECIMAL_DIG, DBL_MAX);
    printf("DBL_EPSILON: %.*e\n", DBL_DECIMAL_DIG, DBL_EPSILON);
    printf("DBL_TRUE_MIN: %.*e\n\n", DBL_DECIMAL_DIG, DBL_TRUE_MIN);

    printf("LDBL_HAS_SUBNORM: %d\n", LDBL_HAS_SUBNORM);
    printf("LDBL_MANT_DIG: %d\n", LDBL_MANT_DIG);
    printf("LDBL_DECIMAL_DIG: %d\n", LDBL_DECIMAL_DIG);
    printf("LDBL_DIG: %d\n", LDBL_DIG);
    printf("LDBL_MIN_EXP: %d\n", LDBL_MIN_EXP);
    printf("LDBL_MIN_10_EXP: %d\n", LDBL_MIN_10_EXP);
    printf("LDBL_MAX_EXP: %d\n", LDBL_MAX_EXP);
    printf("LDBL_MAX_10_EXP: %d\n", LDBL_MAX_10_EXP);
    printf("LDBL_MIN: %.*Le\n", LDBL_DECIMAL_DIG, LDBL_MIN);
    printf("LDBL_MAX: %.*Le\n", LDBL_DECIMAL_DIG, LDBL_MAX);
    printf("LDBL_EPSILON: %.*Le\n", LDBL_DECIMAL_DIG, LDBL_EPSILON);
    printf("LDBL_TRUE_MIN: %.*Le\n\n", LDBL_DECIMAL_DIG, LDBL_TRUE_MIN);
    
    printf("sizeof(float): %zu\n", sizeof(float));
    printf("sizeof(double): %zu\n", sizeof(double));
    printf("sizeof(long double): %zu\n", sizeof(long double));
}

FLT_RADIX: 2
FLT_ROUNDS: 1
FLT_EVAL_METHOD: 0
DECIMAL_DIG: 21

FLT_HAS_SUBNORM: 1
FLT_MANT_DIG: 24
FLT_DECIMAL_DIG: 9
FLT_DIG: 6
FLT_MIN_EXP: -125
FLT_MIN_10_EXP: -37
FLT_MAX_EXP: 128
FLT_MAX_10_EXP: 38
FLT_MIN: 1.175494351e-38
FLT_MAX: 3.402823466e+38
FLT_EPSILON: 1.192092896e-07
FLT_TRUE_MIN: 1.401298464e-45

DBL_HAS_SUBNORM: 1
DBL_MANT_DIG: 53
DBL_DECIMAL_DIG: 17
DBL_DIG: 15
DBL_MIN_EXP: -1021
DBL_MIN_10_EXP: -307
DBL_MAX_EXP: 1024
DBL_MAX_10_EXP: 308
DBL_MIN: 2.22507385850720138e-308
DBL_MAX: 1.79769313486231571e+308
DBL_EPSILON: 2.22044604925031308e-16
DBL_TRUE_MIN: 4.94065645841246544e-324

LDBL_HAS_SUBNORM: 1
LDBL_MANT_DIG: 64
LDBL_DECIMAL_DIG: 21
LDBL_DIG: 18
LDBL_MIN_EXP: -16381
LDBL_MIN_10_EXP: -4931
LDBL_MAX_EXP: 16384
LDBL_MAX_10_EXP: 4932
LDBL_MIN: 3.362103143112093506263e-4932
LDBL_MAX: 1.189731495357231765021e+4932
LDBL_EPSILON: 1.084202172485504434007e-19
LDBL_TRUE_MIN: 3.645199531882474602528e-4951

sizeof(float): 4
sizeof(double): 8
sizeof(long double): 16