c - printf 作为函数的参数

Question

通常使用函数：

my_func("test");

我是否可以这样使用这个参数？

my_func(printf("current_count_%d",ad_id));

int my_func(const char *key)

Answer 1

是的，您可以将 的返回值printf用作函数参数。
但请记住printf，成功返回写入的字符数。
所以

foo(printf("bar%d",123)); 

传递6给foo函数 not bar123。

如果要传递printf打印的字符串，可以使用sprintf函数。它类似于printf但不是写入控制台，而是写入 char 数组。

Answer 2

    char buf[64]; /* malloc or whatever */
    int pos = snprintf(buf, sizeof(buf), "current_count_%d", ad_id);
    if (sizeof(buf) <= pos)
                    buf[sizeof(buf)-1] = '\0';
    my_func(buf)

Answer 3

不; printf()返回打印到标准输出的字符数。用于s[n]printf()创建字符串，然后传递它。

Answer 4

如果您希望将可变数量的参数（例如 printf 接受）传递给某个函数，那么您需要查看 . 重现 printf （为了论证）：

void varargfunc(char *fmt, ...)
{
    char formattedString[2048]; /* fixed length, for a simple example - and
                                   snprintf will keep us safe anyway */
    va_list arguments;

    va_start(arguments, fmt); /* use the parameter before the ellipsis as
                                 a seed */

    /* assuming the first argument after fmt is known to be an integer,
       you could... */
    /*
        int firstArgument = va_arg(arguments, int);
        fprintf(stderr, "first argument was %d", firstArgument);
    */

    /* do an vsnprintf to get the formatted string with the variable
       argument list. The v[printf/sprintf/snprintf/etc] functions
       differ from [printf/sprintf/snprintf/etc] by taking a va_list
       rather than ... - a va_list can't turn back into a ... because
       it doesn't inherently know how many additional arguments it
       represents (amongst other reasons) */
    vsnprintf(formattedString, 2048, fmt, arguments);

    /* formattedString now contains the first 2048 characters of the
       output string, with correct field formatting and a terminating
       NULL, even if the real string would be more than 2047 characters
       long. So put that on stdout. puts adds an additional terminating
       newline character, so this varies a little from printf in that 
       regard. */
    puts(formattedString);

    va_end(arguments); /* clean up */
}

如果您想添加与格式无关的其他参数，请在 'fmt' 参数之前添加它们。Fmt 被传递给 va_start 来表示“变量参数在这个之后开始”。

Answer 5

该函数printf 返回一个整数。

int printf ( const char * format, ... );

因此，my_func只要my_func将整数作为参数，您就可以使用它。情况似乎并非如此。