请问printf( "%.19s %s\n", buff, am_pm )中的."点"起什么作用？

[fhw217]

如题！！！！！！！！

[lx624909677]

格式控制，比如你以%.2lf输出1.23456，就会保留小数点后两位，也就是输出1.23

[lx624909677]

而你那个是.s的格式，就是输出指定个数的字符，比如一个字符串是abcdef，输出用.2s,输出的内容就是ab

[lis2012]

小数点后边的输出位数

[赵4老师]

引用 4 楼 lsq19871207 的回复:

%s 如果加%.ns 表示格式化输出n个字符

%.*s

[赵4老师]

Precision Specification The third optional field of the format specification is the precision specification. It specifies a nonnegative decimal integer, preceded by a period (.), which specifies the number of characters to be printed, the number of decimal places, or the number of significant digits (see Table R.5). Unlike the width specification, the precision specification can cause either truncation of the output value or rounding of a floating-point value. If precision is specified as 0 and the value to be converted is 0, the result is no characters output, as shown below: printf( "%.0d", 0 ); /* No characters output */ If the precision specification is an asterisk (*), an int argument from the argument list supplies the value. The precision argument must precede the value being formatted in the argument list. The type determines the interpretation of precision and the default when precision is omitted s, S The precision specifies the maximum number of characters to be printed. Characters in excess of precision are not printed. Characters are printed until a null character is encountered

[信阳毛尖]

%s 如果加%.ns 表示格式化输出n个字符