C中大小写双（浮点）类型说明符的区别

Question

在C double / float中有一个集类型说明符：%f %F %g %G %e %E。两者之间有什么区别吗？

• %f和%F，
• %g和%G，
• %e和%E？

据printf和scanf说，输出是平等的。那么为什么大小写都有效？

请注意，scanf double的类型说明符以小写l开头

Answer 1

specifier   Output  Example
d or i  Signed decimal integer  392
u   Unsigned decimal integer    7235
o   Unsigned octal  610
x   Unsigned hexadecimal integer    7fa
X   Unsigned hexadecimal integer (uppercase)    7FA
f   Decimal floating point, lowercase   392.65
F   Decimal floating point, uppercase   392.65
e   Scientific notation (mantissa/exponent), lowercase  3.9265e+2
E   Scientific notation (mantissa/exponent), uppercase  3.9265E+2
g   Use the shortest representation: %e or %f   392.65
G   Use the shortest representation: %E or %F   392.65
a   Hexadecimal floating point, lowercase   -0xc.90fep-2
A   Hexadecimal floating point, uppercase   -0XC.90FEP-2
c   Character   a
s   String of characters    sample
p   Pointer address b8000000
n   Nothing printed.
The corresponding argument must be a pointer to a signed int.
The number of characters written so far is stored in the pointed location.  
%   A % followed by another % character will write a single % to the stream.    %

The Source of above

Answer 2

%f和%F之间的区别在于它们是否打印无穷大和NaN为小写或大写。这是一个例子：

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

int main(){
    printf("%f and %f\n", INFINITY, nan("0"));    //Prints "inf and nan"
    printf("%F and %F\n", INFINITY, nan("0"));    //Prints "INF and NAN"
    return 0;
}

打印实数时，%f和%F是相同的。例如，printf("%f", 1.0)和printf("%F", 1.0)完全一样。

请注意，%F仅适用于C99或C ++。

%e和%E之间的区别在于，将数字和指数分开的“e”是低或大写（例如1.0e+0或1.0E+0。对于无穷大和Nan也有区别，就像%f和%F一样。这是一个例：

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

int main(){
    printf("%e, %e and %e\n", INFINITY, nan("0"), 1.0); //Prints "inf, nan and 1.0000e+00"
    printf("%E, %E and %E\n", INFINITY, nan("0"), 1.0); //Prints "INF, NAN and 1.0000E+00"
    return 0;
}

%g和%G之间的差异是%g在%e和%f之间最短，而%G在%E和%F之间最短。