结构体数组中的联合体初始化

2017-05-31 09:35:19 730 阅读 AI 写同款 · GEO 优化AI 选题数据监测一键分发 ›

【SystemVerilog学习笔记】5-数组、结构图和联合体目录5.1 结构体5.1.1 结构体的声明5.1.2 结构体的赋值5.1.3 压缩和非压缩结构体5.1.4 通过端口传递结构体5.1.5 将结构体作为自变量传递至任务和函数5.1.6 综合指导5.2 联合体5.2.1 非压缩联合体5.2.2 标签联合体5.2.3 压缩联合体5.2.4 综合指导5.3 数组5.3.1 非压缩数组5.3.2 压缩数组5.3.3 使用压缩和非压缩数组5.3.4 声明时对数组进行初始化5.3.5 数组赋值5.3.6 数组复制5.3.7 使用位流转换赋值数组和结构体5.3.8 由数组阅读详情

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出现 error C2059: 语法错误 : “.”

...全文

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izardMan

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schlafenhamster 2017-06-04

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{str= "medium" } 不要那个点？

izardMan 2017-06-02

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C99好坑，看来只有用vs2013以上的版本了。

izardMan 2017-06-01

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应该可以指定吧，那些代码是搞开源的大牛写的，但是在vs2008下调试不过，想问问是怎么回事。

「已注销」 2017-06-01

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引用 7 楼 wuzongman 的回复:

应该可以指定吧，那些代码是搞开源的大牛写的，但是在vs2008下调试不过，想问问是怎么回事。

VS2010 很多都不支持，别提 2008 了，这个还是用 gcc 编译，或者用 VS2017 吧。

paschen 2017-05-31

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union只能对第一个元素进行初始化

izardMan 2017-05-31

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感谢赵老师的分享，我想在声明中直接初始化结构体中的联合体，如果是分开初始化。那应该就比较简单了。

赵4老师 2017-05-31

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再供参考：

#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
//
//

赵4老师 2017-05-31

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仅供参考：

#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)

izardMan 2017-05-31

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顶起，不要沉了

izardMan 2017-05-31

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调试FFmpeg出现了该问题，发现基础好弱。

结构体数组中的联合体初始化

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