在C近拍实现putc将（）的

问题描述

我一直在寻找的宏实现putc将（c）中的功能。

I was looking for the macro implementation of putc() function in C.

一个实现我在C编程语言发现由Ritchie和Kernighan的

One implementation which i found in "The C programming language" by Ritchie and Kernighan

#define putc(x,p) (--(p)->cnt >=0 \
                  ?(unsigned char) *(p)->ptr++ :_flushbuf((x),p))

文件结构的定义如下：

The file structure definition is as follows

typedef struct _iobuf {
                int cnt;
                char *ptr;
                char *base;
                int flag;
                int fd;
             }FILE;

我看不到CNT被初始化如何当我们调用putc将？

I am unable to see how cnt gets initialised when we call putc ?

推荐答案

它无疑是的fopen 初始化，并由其他任何读取/文件写入修改。

It's undoubtedly initialized by fopen, and modified by anything else that reads/writes the file.

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