C语言中snprintf sprintf 使用和sizeof和strlen的区别和puts的使用

  char fn[256];
    int rc;

    pcm = calloc(1, sizeof(struct pcm));
    if (!pcm || !config)
        return &bad_pcm; /* TODO: could support default config here */

    pcm->config = *config;

    snprintf(fn, sizeof(fn), "/dev/snd/pcmC%uD%u%c", card, device,
             flags & PCM_IN ? 'c' : 'p');

    pcm->flags = flags;
    pcm->fd = open(fn, O_RDWR);
    if (pcm->fd < 0) {
        oops(pcm, errno, "cannot open device '%s'", fn);
        return pcm;
    }

　　

       

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <pthread.h>
#include <semaphore.h>
#include <unistd.h>
#include <signal.h>
#include <string.h>


// static
static int seq[] = {1,2,3,4,5,6};
static const char* string[] = { "a","b","c","d"};

static char* pstring=  "http://www.ABCD.com";

/**
     char fn[256];
     snprintf(fn, sizeof(fn), "/dev/snd/pcmC%uD%u%c", card, device,
             flags & PCM_IN ? 'c' : 'p');
**/

#define  PCM_IN   (0)
#define  PCM_OUT  (1)

int main()
{
    int i = 0;
    unsigned int card ;
    unsigned int device;
    unsigned int flags;

    char fn[256] = {0};
    sprintf(fn,"/dev/snd/pcmC%uD%u%c",card,device,flags & PCM_IN ? 'c' : 'p');
    //printf("%s\n",fn);
    puts(fn);
    snprintf(fn, sizeof(fn), "/dev/snd/pcmC%uD%u%c", card, device,
             flags & PCM_IN ? 'c' : 'p');
    puts(fn);
    // strlen和sizeof的差距
    printf("%d %d\n",strlen(fn),sizeof(fn)/sizeof(char));
    while(i++<strlen(fn))
    {
        puts(fn);
    }

    while(1);

    return 0;
}