h.264 - Why there is no AVFrame->data[2] data when decode h264 by ffmpeg use "h264_cuvid" -

env: ubuntu 16.04 64 bit; ffmpeg 3.3.2 build whih cuda cuvid libnpp...
use ffmpeg cmd: ffmpeg -vsync 0 -c:v h264_cuvid -i test.264 -f rawvideo test.yuv works fine, generated yuv file ok.
but when decode 264 file code use 'h264_cuvid' decoder, problem happens, code:

#include <stdio.h>  #define __stdc_constant_macros  #ifdef _win32 //windows extern "c" { #include "libavcodec/avcodec.h" }; #else //linux... #ifdef __cplusplus extern "c" { #endif #include <libavcodec/avcodec.h> #ifdef __cplusplus }; #endif #endif   //test different codec #define test_h264  1 #define test_hevc  0  int main(int argc, char* argv[]) {     avcodec *pcodec;     avcodeccontext *pcodecctx= null;     avcodecparsercontext *pcodecparserctx=null;      file *fp_in;     file *fp_out;     avframe *pframe;      const int in_buffer_size=4096;     unsigned char in_buffer[in_buffer_size + ff_input_buffer_padding_size]= {0};     unsigned char *cur_ptr;     int cur_size;     avpacket packet;     int ret, got_picture;   #if test_hevc     enum avcodecid codec_id=av_codec_id_hevc;     char filepath_in[]="bigbuckbunny_480x272.hevc"; #elif test_h264     avcodecid codec_id=av_codec_id_h264;     char filepath_in[]="2_60_265to264.264"; #else     avcodecid codec_id=av_codec_id_mpeg2video;     char filepath_in[]="bigbuckbunny_480x272.m2v"; #endif      char filepath_out[]="mainsend.yuv";     int first_time=1;       //av_log_set_level(av_log_debug);      avcodec_register_all();  //    pcodec = avcodec_find_decoder(codec_id);     pcodec = avcodec_find_decoder_by_name("h264_cuvid");     if (!pcodec)     {         printf("codec not found\n");         return -1;     }     pcodecctx = avcodec_alloc_context3(pcodec);     if (!pcodecctx)     {         printf("could not allocate video codec context\n");         return -1;     }      pcodecparserctx=av_parser_init(pcodec->id);     if (!pcodecparserctx)     {         printf("could not allocate video parser context\n");         return -1;     }      if (avcodec_open2(pcodecctx, pcodec, null) < 0)     {         printf("could not open codec\n");         return -1;     }     //input file     fp_in = fopen(filepath_in, "rb");     if (!fp_in)     {         printf("could not open input stream\n");         return -1;     }     //output file     fp_out = fopen(filepath_out, "wb");     if (!fp_out)     {         printf("could not open output yuv file\n");         return -1;     }      pframe = av_frame_alloc();     av_init_packet(&packet);      while (1)     {          cur_size = fread(in_buffer, 1, in_buffer_size, fp_in);         if (cur_size == 0)             break;         cur_ptr=in_buffer;          while (cur_size>0)         {              int len = av_parser_parse2(                           pcodecparserctx, pcodecctx,                           &packet.data, &packet.size,                           cur_ptr, cur_size,                           av_nopts_value, av_nopts_value, av_nopts_value);              cur_ptr += len;             cur_size -= len;              if(packet.size==0)                 continue;              //some info avcodecparsercontext             printf("[packet]size:%6d\t",packet.size);             switch(pcodecparserctx->pict_type)             {             case av_picture_type_i:                 printf("type:i\tnumber:%4d\n",pcodecparserctx->output_picture_number);                 break;             case av_picture_type_p:                 printf("type:p\t");                 break;             case av_picture_type_b:                 printf("type:b\t");                 break;             default:                 printf("type:other\t");                 break;             }             printf("number:%4d\n",pcodecparserctx->output_picture_number);             avframe* myframe = av_frame_alloc();             ret = avcodec_decode_video2(pcodecctx, myframe, &got_picture, &packet);             if (ret < 0)             {                 printf("decode error.\n");                 return ret;             }             if (got_picture)             {                 if(first_time)                 {                     printf("\ncodec full name:%s\n",pcodecctx->codec->long_name);                     printf("width:%d\nheight:%d\n\n",pcodecctx->width,pcodecctx->height);                     first_time=0;                 }                 //y, u, v                 for(int i=0; i<myframe->height; i++)                 {                     fwrite(myframe->data[0]+myframe->linesize[0]*i,1,myframe->width,fp_out);                 }                 for(int i=0; i<myframe->height/2; i++)                 {                     fwrite(myframe->data[1]+myframe->linesize[1]*i,1,myframe->width/2,fp_out);                 }                 for(int i=0; i<myframe->height/2; i++)                 {                     fwrite(myframe->data[2]+myframe->linesize[2]*i,1,myframe->width/2,fp_out);                 } //                printf("pframe's width height %d %d\t key frame %d\n",myframe->width,myframe->height,myframe->key_frame);                 printf("succeed decode 1 frame!\n");                 av_frame_free(&myframe);             }         }      }      fclose(fp_in);     fclose(fp_out);       av_parser_close(pcodecparserctx);      av_frame_free(&pframe);     avcodec_close(pcodecctx);     av_free(pcodecctx);      return 0; } 

in demo code, call h264_cuvid vcodec_find_decoder_by_name("h264_cuvid"); code crash @ fwrite(myframe->data[2]+myframe->linesize[2]*i,1,myframe->width/2,fp_out);
after debug codeblocks, found there no data in myframe->data[2] codeblocks watching window

any suggestion? thanks!

"h264" decoder's frame pix format av_pix_fmt_yuv420p
"h264_cuvid" decoder's frame pix format av_pix_fmt_nv12
so, edit code

            for(int i=0; i<myframe->height; i++)             {                 fwrite(myframe->data[0]+myframe->linesize[0]*i,1,myframe->width,fp_out);             }             for(int i=0; i<myframe->height/2; i++)             {                 fwrite(myframe->data[1]+myframe->linesize[1]*i,1,myframe->width,fp_out);             } 

works fine