About the man usage

man 3p printf
man 3 printf

The above two man page gives different info of printf.

What's different for man 3开发者_Python百科 and man 3p?

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$ man -k printf | grep '^printf'
printf (1)           - format and print data
printf (1posix)      - write formatted output
printf (3)           - formatted output conversion
printf (3posix)      - print formatted output

You have probably installed the manpages-posix and manpages-posix-dev packages on your system, as I have. This also gives you the POSIX-prepared manpages, which is an excellent way to determine if you're relying on behavior specific to your system or standardized behavior.

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I believe you can find the answer to this yourself with:

man man

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But what is happening is your system defines 3 and 3p as separate sections. This is generally used for "package" man pages, e.g. for the POSIX package.