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man man 

MANUAL SECTIONS
       The standard sections of the manual include:

             User Commands

             System Calls

             C Library Functions

             Devices and Special Files

             File Formats and Conventions

             Games et. Al.

             Miscellanea

             System Administration tools and Deamons

       Distributions customize the manual section to their  specifics,
       which often include additional sections.

例子：

man  printf

PRINTF()                  Linux Programmer’s Manual                 PRINTF()

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, ...);
       int sprintf(char *str, const char *format, ...);
       int snprintf(char *str, size_t size, const char *format, ...);

       #include <stdarg.h>

       int vprintf(const char *format, va_list ap);
       int vfprintf(FILE *stream, const char *format, va_list ap);
       int vsprintf(char *str, const char *format, va_list ap);
       int vsnprintf(char *str, size_t size, const char *format, va_list ap);

   Feature Test Macro Requirements for glibc (see feature_test_macros()):

       snprintf(), vsnprintf(): _BSD_SOURCE || _XOPEN_SOURCE >=  ||
       _ISOC99_SOURCE; or cc -std=c99