'printf' 在 C 中带有前导零 [英] 'printf' with leading zeros in C

问题描述

我有一个浮点数，例如 4917.24.我想把它打印成小数点前总是有五个字符，前导零，然后是小数点后三个数字.

I have a floating point number such as 4917.24. I'd like to print it to always have five characters before the decimal point, with leading zeros, and then three digits after the decimal place.

我在我正在使用的嵌入式系统上尝试了 printf("%05.3f", n)，但它打印了 *****.我的格式说明符是否正确?

I tried printf("%05.3f", n) on the embedded system I'm using, but it prints *****. Do I have the format specifier correct?

推荐答案

您的格式说明符不正确.从我机器上的 printf() 手册页:

Your format specifier is incorrect. From the printf() man page on my machine:

0 零0"字符表示应使用零填充而不是空白 -填充.如果同时使用了-"，则会覆盖0"；

0 A zero '0' character indicating that zero-padding should be used rather than blank-padding. A '-' overrides a '0' if both are used;

字段宽度:指定字段宽度的可选数字字符串；如果输出字符串的字符少于字段宽度，它将在左侧(或右侧，如果已给出左调整指示符)填充空白以弥补字段宽度(请注意，前导零是一个标志，但嵌入的零是字段宽度的一部分)；

Field Width: An optional digit string specifying a field width; if the output string has fewer characters than the field width it will be blank-padded on the left (or right, if the left-adjustment indicator has been given) to make up the field width (note that a leading zero is a flag, but an embedded zero is part of a field width);

精度:一个可选的句点，'.'，后跟一个可选的数字字符串，给出一个精度，指定出现在小数点后的位数，例如e 和 f 格式，或从字符串中打印的最大字符数；如果缺少数字字符串，则将精度视为零；

Precision: An optional period, '.', followed by an optional digit string giving a precision which specifies the number of digits to appear after the decimal point, for e and f formats, or the maximum number of characters to be printed from a string; if the digit string is missing, the precision is treated as zero;

对于您的情况，您的格式为 %09.3f:

For your case, your format would be %09.3f:

#include <stdio.h>

int main(int argc, char **argv)
{
  printf("%09.3f
", 4917.24);
  return 0;
}

输出:

$ make testapp
cc     testapp.c   -o testapp
$ ./testapp 
04917.240

请注意，此答案取决于您的嵌入式系统是否具有符合这些细节标准的 printf() 实现 - 许多嵌入式环境没有实施.

Note that this answer is conditional on your embedded system having a printf() implementation that is standard-compliant for these details - many embedded environments do not have such an implementation.

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