各位亲们，程序中有几个语句看不懂，求救啊！！！

769817084 · 发表于 2013-3-6 22:33:01

今天看到一个程序中有下面3个模块，但不知道是什么意思，为什么要写这些语句？
（1）#ifdef USE_STM3210B_EVAL
#include "stm3210b_eval_lcd.h"
#elif defined USE_STM3210E_EVAL
#include "stm3210e_eval_lcd.h"
#elif defined USE_STM3210C_EVAL
#include "stm3210c_eval_lcd.h"
#endif

（2）#ifdef USE_STM3210B_EVAL
#define MESSAGE1   "STM32 Medium Density"
#define MESSAGE2   " Device running on "
#define MESSAGE3   "   STM3210B-EVAL    "
#elif defined USE_STM3210E_EVAL
#define MESSAGE1   " STM32 High Density "
#define MESSAGE2   " Device running on "
#define MESSAGE3   "   STM3210E-EVAL    "
#elif defined USE_STM3210C_EVAL
#define MESSAGE1   " STM32 Connectivity "
#define MESSAGE2   " Line Device running"
#define MESSAGE3   " on STM3210C-EVAL   "
#endif

（3）#ifdef __GNUC__
#define PUTCHAR_PROTOTYPE int __io_putchar(int ch)
#else
#define PUTCHAR_PROTOTYPE int fputc(int ch, FILE *f)
#endif

这3个模块的语句都看不懂，请各位帮帮忙！