每次想查某个C库函数的文件时，总是上网搜，然后在博客里看到。有是还得看好几篇，才找到。

这不是办法呀，window有MSDN，linux有MAN，怎么不去用呢？

1. 查看man(manual)手册说明，看，man既是动词，又是名词，它还是形容词（他好man哦）

$ man man

       The table below shows the section numbers of the manual followed by the types of pages they contain.

       1   Executable programs or shell commands
       2   System calls (functions provided by the kernel)
       3   Library calls (functions within program libraries)
       4   Special files (usually found in /dev)
       5   File formats and conventions eg /etc/passwd
       6   Games
       7   Miscellaneous (including macro packages and conventions), e.g. man(7), groff(7)
       8   System administration commands (usually only for root)
       9   Kernel routines [Non standard]

可以看到，第3条是显示库函数的手册。

2. 查看printf头文件

$ man 3 printf

查看格式化说明符，可以搜索specifier

   The conversion specifier
       A character that specifies the type of conversion to be applied.  The conversion specifiers and their meanings are:

       d, i   The  int  argument is converted to signed decimal notation.  The precision, if any, gives the minimum number of digits that must appear; if the converted value
              requires fewer digits, it is padded on the left with zeros.  The default precision is 1.  When 0 is printed with an explicit precision 0, the output is empty.

       o, u, x, X
              The unsigned int argument is converted to unsigned octal (o), unsigned decimal (u), or unsigned hexadecimal (x and X) notation.  The letters  abcdef  are  used
              for x conversions; the letters ABCDEF are used for X conversions.  The precision, if any, gives the minimum number of digits that must appear; if the converted
              value requires fewer digits, it is padded on the left with zeros.  The default precision is 1.  When 0 is printed with an explicit precision 0, the  output  is
              empty.

查看所在头文件，就在开头SYNOPSIS标题下

PRINTF(3)                                                                 Linux Programmer's Manual                                                                 PRINTF(3)

NAME
       printf, fprintf, sprintf, snprintf, vprintf, vfprintf, vsprintf, vsnprintf - formatted output conversion

SYNOPSIS
       #include <stdio.h>

       int printf(const char *format, ...);
       int fprintf(FILE *stream, const char *format, ...);

如果直接：

$ man printf

则默认显示的是第1条：可执行程序或shell命令

1 Executable programs or shell commands