％m格式说明符是什么意思? [英] What's the meaning of the %m formatting specifier?

问题描述

此代码的输出打印为成功".

printf("%m\n");

解决方案

m转换说明符不是C，而是对printf的GNU扩展:

来自GNU文档:

http://www.gnu.org/软件/libc/manual/html_node/Other-Output-Conversions.html

％m"转换会打印与errno中的错误代码相对应的字符串.请参阅错误消息.因此:

fprintf (stderr, "can't open `%s': %m\n", filename);

等效于:

fprintf (stderr, "can't open `%s': %s\n", filename, strerror (errno));

％m"转换是GNU C库扩展.

所以:

printf("%m\n", d);

等同于

printf("%s\n", strerror (errno), d);

等效于

printf("%s\n", strerror (errno));

请注意，%m不需要参数.这里的printf("%m\n", d)和printf("%s\n", strerror (errno), d)具有比所需更多的参数:使用printf时，如果有多余的尾随参数，则它们将被求值并忽略.

The output for this code printed out ‘Success’.

printf("%m\n");

解决方案

m conversion specifier is not C but is a GNU extension to printf:

From GNU documentation:

http://www.gnu.org/software/libc/manual/html_node/Other-Output-Conversions.html

The ‘%m’ conversion prints the string corresponding to the error code in errno. See Error Messages. Thus:

fprintf (stderr, "can't open `%s': %m\n", filename);

is equivalent to:

fprintf (stderr, "can't open `%s': %s\n", filename, strerror (errno));

The ‘%m’ conversion is a GNU C Library extension.

So:

printf("%m\n", d);

is equivalent to

printf("%s\n", strerror (errno), d);

which is equivalent to

printf("%s\n", strerror (errno));

Note that %mdoes not require an argument. Here printf("%m\n", d) and printf("%s\n", strerror (errno), d) have more arguments than required: with printf if there are extra trailing arguments, they are just evaluated and ignored.

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