【求助】代码中的这个用法是什么意思

2019-03-26 12:29发布

8775 5

各位大神大家好，目前在阅读代码时，发现有这么一个用法【f->keep_last = !!keep_last;】这个【!!】是个什么意思？这么用有什么好处呢？

static int frame_queue_init(FrameQueue *f, PacketQueue *pktq, int max_size, int keep_last)
{
int i;
memset(f, 0, sizeof(FrameQueue));
if (!(f->mutex = SDL_CreateMutex())) {
av_log(NULL, AV_LOG_FATAL, "SDL_CreateMutex(): %s ", SDL_GetError());
return AVERROR(ENOMEM);
}
if (!(f->cond = SDL_CreateCond())) {
av_log(NULL, AV_LOG_FATAL, "SDL_CreateCond(): %s ", SDL_GetError());
return AVERROR(ENOMEM);
}
f->pktq = pktq;
f->max_size = FFMIN(max_size, FRAME_QUEUE_SIZE);
f->keep_last = !!keep_last;
for (i = 0; i < f->max_size; i++)
if (!(f->queue[i].frame = av_frame_alloc()))
return AVERROR(ENOMEM);
return 0;
}