C语言 printf中的“%.*s”是什么意思?
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What does "%.*s" mean in printf?
提问by Shaobo Wang
I got a code snippet in which there is a
我有一个代码片段,其中有一个
printf("%.*s\n")
what does the %.*smean?
是什么%.*s意思?
回答by AusCBloke
回答by Ondrej
More detailed here.
更详细的在这里。
integer value or
*that specifies minimum field width. The result is padded with space characters (by default), if required, on the left when right-justified, or on the right if left-justified. In the case when * is used, the width is specified by an additional argument of type int. If the value of the argument is negative, it results with the - flag specified and positive field width. (Note: This is the minimum width: The value is never truncated.)
.followed by integer number or *, or neither that specifies precision of the conversion. In the case when * is used, the precision is specified by an additional argument of type int. If the value of this argument is negative, it is ignored. If neither a number nor * is used, the precision is taken as zero. See the table below for exact effects of precision.
整数值或
*指定最小字段宽度。结果用空格字符填充(默认情况下),如果需要,右对齐时在左侧,如果左对齐则在右侧。在使用 * 的情况下,宽度由 int 类型的附加参数指定。如果参数的值为负,则结果为 - 指定的标志和正的字段宽度。(注意:这是最小宽度:该值永远不会被截断。)
.后跟整数或 *,或两者都不指定转换的精度。在使用 * 的情况下,精度由 int 类型的附加参数指定。如果此参数的值为负,则将其忽略。如果既不使用数字也不使用 *,则精度为零。有关精度的确切影响,请参见下表。
So if we try both conversion specification
所以如果我们尝试两种转换规范
#include <stdio.h>
int main() {
int precision = 8;
int biggerPrecision = 16;
const char *greetings = "Hello world";
printf("|%.8s|\n", greetings);
printf("|%.*s|\n", precision , greetings);
printf("|%16s|\n", greetings);
printf("|%*s|\n", biggerPrecision , greetings);
return 0;
}
we get the output:
我们得到输出:
|Hello wo|
|Hello wo|
| Hello world|
| Hello world|
回答by rerun
I don't think the code above is correct but (according to this description of printf()) the .*means
我不认为上面的代码是正确的,但是(根据这个描述printf()).*意味着
The width is not specified in the format string, but as an additional integer value argument preceding the argument that has to be formatted.'
宽度未在格式字符串中指定,而是作为必须格式化的参数之前的附加整数值参数。
So it's a string with a passable width as an argument.
所以它是一个具有可传递宽度的字符串作为参数。
回答by Josh
See: http://www.cplusplus.com/reference/clibrary/cstdio/printf/
见:http: //www.cplusplus.com/reference/clibrary/cstdio/printf/
.*The precision is not specified in the format string, but as an additional integer value argument preceding the argument that has to be formatted.
sString of characters
.*精度未在格式字符串中指定,而是作为必须格式化的参数之前的附加整数值参数。
s字符串

