根据用户偏好进行过滤的包装 printf 函数 [英] wrapper printf function that filters according to user preferences

问题描述

我的程序写入日志和标准输出.然而，每条消息都有一个特定的优先级，用户在首选项中指定哪些优先级属于哪个流(日志或标准输出).

My program writes to a log and to stdout. Every message, however, has a certain priority and the user specifies in Preferences which priorities go to which stream (log or stdout).

unsigned short PRIO_HIGH = 0x0001;
unsigned short PRIO_NORMAL = 0x0002;
unsigned short PRIO_LOW = 0x0004;

偏好由一些标志处理:

unsigned short PRIO_LOG = (PRIO_HIGH | PRIO_NORMAL);
unsigned short PRIO_STD = (PRIO_HIGH);

write_log 函数应该使用与 printf 函数相同的参数，但增加了 unsigned short priority 参数.

The write_log function should work with the same parameters as the printf function, with the added parameter of unsigned short priority.

write_log((PRIO_NORMAL|PRIO_LOW), "HELLO %s, take %d", "World", 1);

(即使 PRIO_NORMAL|PRIO_LOW 毫无意义...)

(Even if PRIO_NORMAL|PRIO_LOW makes little sense...)

检查标志很容易:if(priority & PRIO_LOG)(如果在两个参数中都设置了任何标志，则返回 >1)

Checking the flags is easy: if(priority & PRIO_LOG) (Returns >1 if any flag is set in both arguments)

然而，我不知道如何将字符串文字 和 格式参数传递给 printf 函数.任何人都可以帮助或给我一个指针(可能是达到相同效果的替代方法)?将不胜感激.

I cannot however find out how I would go about passing the string literal and the format arguments to the printf function. Can anyone help or give me a pointer (possible to an alternative method that achieves the same effect)? It would be much appreciated.

推荐答案

您想使用可变参数 "varargs" C 的能力.

You want to call vprintf() instead of printf() using the variable arguments "varargs" capabilities of C.

#include <stdarg.h>

int write_log(int priority, const char *format, ...)
{
    va_list args;
    va_start(args, format);

    if(priority & PRIO_LOG)
            vprintf(format, args);

    va_end(args);
}

有关详细信息，请参阅this.

For more information, see something along the lines of this.

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