这似乎是一个愚蠢的问题，但我陷入了一个问题。请帮帮我。
我正在寻找一种限制双精度数不能以指数形式表示的方法。
我尝试了很多方法，但最后我要在这里问这个。
我的价值是4.2178564565256236e-10
但是我需要15的精度，例如0.00000000042178
使用stdio.h库，printf
参数格式包含要写入标准输出的文本的C字符串。它可以选择包含嵌入式格式说明符，这些格式说明符将替换为后续附加参数中指定的值，并按要求设置格式。
格式说明符遵循此原型：[请参见下面的兼容性说明]
%[flags][width][.precision][length]specifier
结尾处的说明符是最重要的组成部分，因为它定义了类型及其相应参数的解释：说明符输出示例
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.
格式说明符还可以包含子说明符：flags, width, .precision and modifiers (in that order)是可选的，并遵循以下规范：
标志说明
- Left-justify within the given field width; Right justification is the default (see width sub-specifier).
+ Forces to preceed the result with a plus or minus sign (+ or -) even for positive numbers. By default, only negative numbers are preceded with a - sign.
(space) If no sign is going to be written, a blank space is inserted before the value.
# Used with o, x or X specifiers the value is preceeded with 0, 0x or 0X respectively for values different than zero.
Used with a, A, e, E, f, F, g or G it forces the written output to contain a decimal point even if no more digits follow. By default, if no digits follow, no decimal point is written.
0 Left-pads the number with zeroes (0) instead of spaces when padding is specified (see width sub-specifier).
width description
(number) Minimum number of characters to be printed. If the value to be printed is shorter than this number, the result is padded with blank spaces. The value is not truncated even if the result is larger.
* The width is not specified in the format string, but as an additional integer value argument preceding the argument that has to be formatted.
.precision description
.number For integer specifiers (d, i, o, u, x, X): precision specifies the minimum number of digits to be written. If the value to be written is shorter than this number, the result is padded with leading zeros. The value is not truncated even if the result is longer. A precision of 0 means that no character is written for the value 0.
For a, A, e, E, f and F specifiers: this is the number of digits to be printed after the decimal point (by default, this is 6).
For g and G specifiers: This is the maximum number of significant digits to be printed.
For s: this is the maximum number of characters to be printed. By default all characters are printed until the ending null character is encountered.
If the period is specified without an explicit value for precision, 0 is assumed.
.* The precision is not specified in the format string, but as an additional integer value argument preceding the argument that has to be formatted.
length子说明符修改数据类型的长度。这是一个图表，显示了用于解释带或不带长度说明符的相应参数的类型（如果使用其他类型，则如果允许，则执行正确的类型提升或转换）：
specifiers
length d i u o x X f F e E g G a A c s p n
(none) int unsigned int double int char* void* int*
hh signed char unsigned char signed char*
h short int unsigned short int short int*
l long int unsigned long int wint_t wchar_t* long int*
ll long long int unsigned long long int long long int*
j intmax_t uintmax_t intmax_t*
z size_t size_t size_t*
t ptrdiff_t ptrdiff_t ptrdiff_t*
L long double
关于c指示符的说明：它接受一个int（或wint_t）作为参数，但是在格式化它以进行输出之前将其正确转换为char值（或wchar_t）。
取决于格式字符串，函数可能需要一系列附加参数，每个参数都包含一个用于替换格式字符串中的格式说明符的值（或指向n的存储位置的指针）。这些参数至少应与格式说明符中指定的值数量一样多。该函数将忽略其他参数。
如果成功返回价值写入的字符总数