typedef struct AVOption {
const char *name;
const char *help;
int offset;
enum AVOptionType type;
union {
int64_t i64;
double dbl;
const char *str;
/* TODO those are unused now */
AVRational q;
} default_val;
double min; ///< minimum valid value for the option
double max; ///< maximum valid value for the option
int flags;
#define AV_OPT_FLAG_ENCODING_PARAM 1 ///< a generic parameter which can be set by the user for muxing or encoding
#define AV_OPT_FLAG_DECODING_PARAM 2 ///< a generic parameter which can be set by the user for demuxing or decoding
#if FF_API_OPT_TYPE_METADATA
#define AV_OPT_FLAG_METADATA 4 ///< some data extracted or inserted into the file like title, comment, ...
#endif
#define AV_OPT_FLAG_AUDIO_PARAM 8
#define AV_OPT_FLAG_VIDEO_PARAM 16
#define AV_OPT_FLAG_SUBTITLE_PARAM 32
#define AV_OPT_FLAG_EXPORT 64
#define AV_OPT_FLAG_READONLY 128
#define AV_OPT_FLAG_FILTERING_PARAM (1<<16) ///< a generic parameter which can be set by the user for filtering
const char *unit;
} AVOption;
static const AVOption options[] = {
{ "preset", "Set the encoding preset (cf. x264 --fullhelp)", OFFSET(preset), AV_OPT_TYPE_STRING, {.str= "medium" }, 0, 0, VE},
{ "tune", "Tune the encoding params (cf. x264 --fullhelp)", OFFSET(tune), AV_OPT_TYPE_STRING, { 0 }, 0, 0, VE},
{ "profile", "Set profile restrictions (cf. x264 --fullhelp) ", OFFSET(profile), AV_OPT_TYPE_STRING, { 0 }, 0, 0, VE},
{ "fastfirstpass", "Use fast settings when encoding first pass", OFFSET(fastfirstpass), AV_OPT_TYPE_BOOL, { .i64 = 1 }, 0, 1, VE}}
初始化.str和.i64出現 error C2059: 語法錯誤 : “.”
uj5u.com熱心網友回復：
除錯FFmpeg出現了該問題，發現基礎好弱。uj5u.com熱心網友回復：
頂起，不要沉了uj5u.com熱心網友回復：
僅供參考：#include <stdio.h>
#include <stdlib.h>
char buf[17];
union U {
unsigned short int aa;
struct {
unsigned int bb:7;//(bit 0-6)
unsigned int cc:6;//(bit 7-12)
unsigned int dd:3;//(bit 13-15)
};
} u;
void main() {
//bbbbbbbbbbbbbbbb
//iiiiiiiiiiiiiiii
//tttttttttttttttt
//111111
//5432109876543210
//::::::::::::::::
u.aa=0xE07F;//1110000001111111
printf("bb==%d,cc==%d,dd==%d\n",u.bb,u.cc,u.dd);
u.bb=0x41;
u.cc=0x21;//dddccccccbbbbbbb
u.dd=5; //1011000011000001
printf("aa==0x%04X==%016s(2)\n",u.aa,itoa(u.aa,buf,2));
}
//bb==127,cc==0,dd==7
//aa==0xB0C1==1011000011000001(2)
uj5u.com熱心網友回復：
再供參考：#include <stdio.h>
#define field_offset(s,f) (int)(&(((struct s *)(0))->f))
struct AD { int a; char b[13]; double c;};
#pragma pack(push)
#pragma pack(1)
struct A1 { int a; char b[13]; double c;};
#pragma pack(2)
struct A2 { int a; char b[13]; double c;};
#pragma pack(4)
struct A4 { int a; char b[13]; double c;};
#pragma pack(8)
struct A8 { int a; char b[13]; double c;};
#pragma pack(16)
struct A16 { int a; char b[13]; double c;};
#pragma pack(pop)
int main() {
printf("AD.a %d\n",field_offset(AD,a));
printf("AD.b %d\n",field_offset(AD,b));
printf("AD.c %d\n",field_offset(AD,c));
printf("AD sizeof %d\n", sizeof(AD));
printf("\n");
printf("A1.a %d\n",field_offset(A1,a));
printf("A1.b %d\n",field_offset(A1,b));
printf("A1.c %d\n",field_offset(A1,c));
printf("A1 sizeof %d\n", sizeof(A1));
printf("\n");
printf("A2.a %d\n",field_offset(A2,a));
printf("A2.b %d\n",field_offset(A2,b));
printf("A2.c %d\n",field_offset(A2,c));
printf("A2 sizeof %d\n", sizeof(A2));
printf("\n");
printf("A4.a %d\n",field_offset(A4,a));
printf("A4.b %d\n",field_offset(A4,b));
printf("A4.c %d\n",field_offset(A4,c));
printf("A4 sizeof %d\n", sizeof(A4));
printf("\n");
printf("A8.a %d\n",field_offset(A8,a));
printf("A8.b %d\n",field_offset(A8,b));
printf("A8.c %d\n",field_offset(A8,c));
printf("A8 sizeof %d\n", sizeof(A8));
printf("\n");
printf("A16.a %d\n",field_offset(A16,a));
printf("A16.b %d\n",field_offset(A16,b));
printf("A16.c %d\n",field_offset(A16,c));
printf("A16 sizeof %d\n", sizeof(A16));
printf("\n");
return 0;
}
//AD.a 0
//AD.b 4
//AD.c 24
//AD sizeof 32
//
//A1.a 0
//A1.b 4
//A1.c 17
//A1 sizeof 25
//
//A2.a 0
//A2.b 4
//A2.c 18
//A2 sizeof 26
//
//A4.a 0
//A4.b 4
//A4.c 20
//A4 sizeof 28
//
//A8.a 0
//A8.b 4
//A8.c 24
//A8 sizeof 32
//
//A16.a 0
//A16.b 4
//A16.c 24
//A16 sizeof 32
//
//
uj5u.com熱心網友回復：
感謝趙老師的分享，我想在宣告中直接初始化結構體中的聯合體，如果是分開初始化。那應該就比較簡單了。uj5u.com熱心網友回復：
union只能對第一個元素進行初始化uj5u.com熱心網友回復：
應該可以指定吧，那些代碼是搞開源的大牛寫的，但是在vs2008下除錯不過，想問問是怎么回事。uj5u.com熱心網友回復：
VS2010 很多都不支持，別提 2008 了，這個還是用 gcc 編譯，或者用 VS2017 吧。uj5u.com熱心網友回復：
C99好坑，看來只有用vs2013以上的版本了。uj5u.com熱心網友回復：
{str= "medium" } 不要那個點 ？轉載請註明出處，本文鏈接：https://www.uj5u.com/gongcheng/98265.html
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