PHP中sprintf、printf等字符串格式化输出中的格式规则总结

sprintf、printf输出格式化字符串。

比如sprintf()的函数原型如下：

string sprintf ( string $format [, mixed $args [, mixed $... ]] )

其中$format用于指定输出的字符串的格式。

进过总结$format遵守以下原型：

%[n$][flags][width][.precision]specifier

其中：

• n$　　　　是position specifier，指明本占位符代表的是哪个参数
  

  <?php
  $num = 5;
  $location = ‘tree‘;
  
  $format = ‘The %2$s contains %1$d monkeys‘;
  echo sprintf($format, $num, $location);

• flags　　　　是一些标志，用来表明是否显示+号、填充字符、对齐方式。具体flags见下表
  

  flag	描述
  +	默认情况下，只有在数字为负数时，才会显示出符号位‘-’。如果数字为正数，则不显示符号位‘+’。本flag设置之后，不论数字为正或为负，都显示符号位。
  ‘sign 或者 0	本flag用来设置用来填充的符号。填充符号是为了是输出的字符串达到width指定的长度。默认的填充符是空格。标准的指定填充符的方式是：单引号+填充符，不过对于0作为填充符，即 可以使用标准定义，也可以直接申明。
  -	本flag用来指明输出的结果是左对齐还是右对齐。缺省下是右对齐，申明本flag后，为左对齐。

  <?php
  echo sprintf ("|%+4d|%+4d|\n",   1, -1);
  echo sprintf ("|%-4d|%-4d|\n",   1, -1);
  echo sprintf ("|%+-4d|%+-4d|\n", 1, -1);
  
  /*
  outputs:
  |  +1|  -1|
  |1   |-1  |
  |+1  |-1  |
  
  */
  
  echo sprintf ("|%04d|\n",   -2);
  echo sprintf ("|%‘:4d|\n",  -2);
  echo sprintf ("|%-‘:4d|\n", -2);
  
  /*
  outputs:
  |-002|
  |::-2|
  |-2::|
  */

• width　　　　指明本格式输出至少有多少字符。即指明字符的输出长度。见上例。
• .precision　　指明对于浮点数，应该保留几位小数

  <?php
  $money = 123.1234;
  echo sprintf("%.2f", $money);    //123.1

• specifier　　specifier指明应该将参数以何种参数类型对待。
  
  

  <?php
  $n =  43951789;
  $u = -43951789;
  $c = 65; // ASCII 65 is ‘A‘
  
  // notice the double %%, this prints a literal ‘%‘ character
  printf("%%b = ‘%b‘\n", $n); // binary representation
  printf("%%c = ‘%c‘\n", $c); // print the ascii character, same as chr() function
  printf("%%d = ‘%d‘\n", $n); // standard integer representation
  printf("%%e = ‘%e‘\n", $n); // scientific notation
  printf("%%u = ‘%u‘\n", $n); // unsigned integer representation of a positive integer
  printf("%%u = ‘%u‘\n", $u); // unsigned integer representation of a negative integer
  printf("%%f = ‘%f‘\n", $n); // floating point representation
  printf("%%o = ‘%o‘\n", $n); // octal representation
  printf("%%s = ‘%s‘\n", $n); // string representation
  printf("%%x = ‘%x‘\n", $n); // hexadecimal representation (lower-case)
  printf("%%X = ‘%X‘\n", $n); // hexadecimal representation (upper-case)
  
  printf("%%+d = ‘%+d‘\n", $n); // sign specifier on a positive integer
  printf("%%+d = ‘%+d‘\n", $u); // sign specifier on a negative integer
  
  %b = ‘10100111101010011010101101‘
  %c = ‘A‘
  %d = ‘43951789‘
  %e = ‘4.39518e+7‘
  %u = ‘43951789‘
  %u = ‘4251015507‘
  %f = ‘43951789.000000‘
  %o = ‘247523255‘
  %s = ‘43951789‘
  %x = ‘29ea6ad‘
  %X = ‘29EA6AD‘
  %+d = ‘+43951789‘
  %+d = ‘-43951789‘

  specifier	Output	Example
  d	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
  c	the argument is treated as an integer, and presented as the character with that ASCII value	a
  s	String of characters	sample
  p	the argument is treated as an integer, and presented as a binary number	10100011
  %	A % followed by another % character will write a single % to the stream.	%

  注明：
  本文主要参考官方文档：http://php.net/manual/en/function.sprintf.php 。并对文档进行了总结，以及对文档部分有偏差部分的纠正。不同处如下：
  1. flags可以是无序的。并不像文档所说——需要按照固定的顺序。flags处的例子可以说明问题。（另外需要指出的是：填充符0和左对齐标志‘-’合用会产生意想不到的结果，见下面的例子）

  echo sprintf ("|%-04d|\n",  -2);　　//输出：     |-2  |