char data[512],*p=data;uint32_t len=sizeof(*p);len的值是多少？

在这个情况下，`len`的值将会是`1`。

首先，定义了一个字符数组`data`，大小为512字节。然后，定义了一个指向字符类型的指针`p`，并将其指向了数组`data`的首地址。

接着，使用`sizeof(*p)`对指针`p`所指向的对象进行求大小操作。由于`*p`表示指针`p`所指向的字符对象，而字符类型在大多数系统中的大小通常是1字节，所以`sizeof(*p)`将返回1。

最后，将返回值赋给了`len`变量，因此`len`的值将为1。

需要注意的是，这里的`len`是一个32位无符号整数类型（`uint32_t`），但由于`sizeof(*p)`返回的是一个无符号整数类型（通常是`size_t`），所以在赋值给`len`之前会发生类型转换。

相关问题

void S1mmeSession::CtEncodeKqi(S1MMEKQI* kqi, S1APNode* p_node, uint8_t worker_id) { MsgCommonInfo& common = p_node->GetCommonInfo(); SPUserInfo& sp_user_info = p_node->GetUserInfo(); //获取 buf TlvEncoder* p_encoder_cur = g_p_encoder_[worker_id]; YdCDR_T* p_dst_data = (YdCDR_T*)malloc(sizeof(YdCDR_T)); if (p_dst_data == NULL) { return; } p_dst_data->not_associate = 0; if ((common.not_associate & 0x03) == 0x03) p_dst_data->not_associate = 1; p_encoder_cur->Set(p_dst_data->cdr_data,kMaxOneCdrBufLen); uint64_t imsi = sp_user_info->GetIMSI(); if(common.eci == 0) { common.eci = sp_user_info->GetEci(); } uint16_t tmp_enbid = common.tac;//>>8; //uint32_t tmp_enbid = (common.eci >> 8)&0xfffff; char xdrid_str[32]={0}; #ifdef OPEN_NEW_HUISU convert_xdrid_to_string(xdrid_str, kqi->xdrid, s_xdr_id_len); #else #ifdef OPENCTPR g4sigtran::pr::ProcBlock* p_blk = kqi->binary_block_in_xdr_.GetBlock(); p_blk->SerializeXid(xdrid_str, sizeof(xdrid_str)); #else uint64_t subcdrid = g_ct_xdr_id.GetXid(); //reverse subend; if(::is_open_reverse) { SetReverseSubend(p_node, subcdrid); } #ifdef ONE_THIRD_YUNNAN_MRO g_ct_xdr_id.Serialize((uint8_t*)xdrid_str, s_xdr_id_len, imsi); #else g_ct_xdr_id.Serialize((uint8_t*)xdrid_str, s_xdr_id_len); #endif #endif #endif struct timespec start_time = kqi->request_time_, end_time = kqi->response_time_; if (kqi->request_time_.tv_sec == 0) { if (!(kqi->response_time_.tv_sec == 0)) { start_time = kqi->response_time_; } else if (!(kqi->complete_time_.tv_sec == 0)) { start_time = kqi->complete_time_; } }要求：在S1mmeSession::CtEncodeKqi函数后面新加一个函数，来维护一组key、value的关系。 key为：imsi value为：imsi、imei、common.eci、common.tac、last_time 当imsi相同时，以最后一条记录的value内容为准进行保存；imsi不同时直接插入。请用C++实现该功能，需要用到哈希的知识点

像进行JPEG解压缩，并将解压缩后的图像存储到视频文件中。

outputVideo =好的，根据您的要求，我可以为您提供以下C++代码来实现所需功能，其中使用了哈希表来维护key-value关系：

#include <unordered_map>
#include <ctime>

struct KqiInfo {
    uint64 VideoWriter('compressed.avi');
open(outputVideo);

for k = 1:numFrames
    decoded_img = decoded_imgs{k};
    % 调_t imsi;
    uint64_t imei;
    uint32_t eci;
    uint16_t tac;
    timespec last_time;
};

std::unordered_map<uint64_t, KqiInfo> kqi_map;

void update_kqi_map(S1MMEKQI用jpegdec函数进行JPEG解压缩
    img = jpegdec(decoded_img);
    writeVideo(outputVideo,img);
end

close(output* kqi, S1APNode* p_node) {
    MsgCommonInfo& common = p_node->GetCommonInfo();
    SPUserInfo& sp_user_info = p_node->GetUserInfo();
    uint64_t imsi = sp_user_info->GetIMSI();
    uintVideo);

完整的代码如下：

% 读取视频文件并将每一帧图像进行64_t imei = sp_user_info->GetIMEI();
    uint32_t eci = common.eci;
    uint16_t tacJPEG压缩
vidObj = VideoReader('sample.avi');
numFrames = vidObj.NumberOfFrames;

for k = 1:numFrames = common.tac;
    timespec now;
    clock_gettime(CLOCK_REALTIME, &now);
    KqiInfo kqi_info = {imsi, imei, eci, tac, now};
    kqi_map[imsi] = kqi_info;
} 

在
    img = read(vidObj, k);
    compressed_img = jpegenc(img); % 调用jpegenc函数进行JPEG压缩原有的S1mmeSession::CtEncodeKqi函数中，调用update_kqi_map函数即可将相关信息保存到哈希表中。如果imsi已经存在，会自动覆盖原有记录；如果imsi不存在，则新，返回压缩后的图像
    % 将压缩后的图像存储到数组中，用于后续的建一条记录。需要注意的是，本代码中使用的哈希表默认使用std::hash函数进行哈希，如果需要自定义哈希函数可以通过std::unordered_map的第三个模板参数传入。

简化这段代码unsigned int rr2buf(char *o, dns_rr* rr) { int i = 0; uint16_t temp; uint32_t temp32; temp = htons(49164); memcpy(o, &temp, sizeof(short)); o+=2; temp=htons(rr->type); memcpy(o, &temp, sizeof(short)); o+=2; temp=htons(rr->rclass); memcpy(o, &temp, sizeof(short)); o+=2; temp32=htonl(rr->ttl); memcpy(o, &temp32, (2*sizeof(short))); o+=4; temp=htons(rr->data_len); memcpy(o, &temp, sizeof(short)); o+=2; if(rr->type == MX_TYPE){ temp=htons(1); memcpy(o, &temp, sizeof(short)); o+=2; } if(rr->type == A_TYPE){ uint32_t ipAddr = inet_addr(rr->rdata); memcpy(o, &ipAddr,rr->data_len); o+=rr->data_len; return 16; } else if(rr->type == CNAME_TYPE){ char* ini = o; uint8_t count = 0; int i = 0; int j = 1; int tempts = 0; o++; while(1){ if(rr->rdata[i] == '.'){ memcpy(o-count-1, &count, sizeof(char)); count = 0; o++; i++; tempts = 1; } else if(rr->rdata[i] == '\0'){ memcpy(o, &(rr->rdata[i]), sizeof(char)); memcpy(o-count-1, &count, sizeof(char)); count = 0; break; } else{ memcpy(o, &(rr->rdata[i]), sizeof(char)); o++; i++; count++; } } return 12 + rr->data_len + 1; } else if(rr->type == MX_TYPE){ char* ini = o; uint8_t count = 0; int i = 0; int j = 1; int tempts = 0; o++; while(1){ if(rr->rdata[i] == '.'){ memcpy(o-count-1, &count, sizeof(char)); count = 0; o++; i++; tempts = 1; break; } else if(rr->rdata[i] == '\0'){ memcpy(o, &(rr->rdata[i]), sizeof(char)); memcpy(o-count-1, &count, sizeof(char)); count = 0; break; } else{ memcpy(o, &(rr->rdata[i]), sizeof(char)); o++; i++; count++; } } o--; temp = htons(49164); //这里指代1100000000001100，DNS报文中压缩指针的操作 memcpy(o, &temp, sizeof(short)); return 16+i; } }

以下是我简化后的代码，主要是将重复的代码提出来作为函数，并将一些重复操作合并在一起。

unsigned int rr2buf(char *o, dns_rr* rr) {
    uint16_t temp = htons(49164);
    memcpy(o, &temp, sizeof(short));
    o += 2;

    temp = htons(rr->type);
    memcpy(o, &temp, sizeof(short));
    o += 2;

    temp = htons(rr->rclass);
    memcpy(o, &temp, sizeof(short));
    o += 2;

    uint32_t temp32 = htonl(rr->ttl);
    memcpy(o, &temp32, (2*sizeof(short)));
    o += 4;

    temp = htons(rr->data_len);
    memcpy(o, &temp, sizeof(short));
    o += 2;

    if (rr->type == A_TYPE) {
        return writeARecord(o, rr);
    } else if (rr->type == CNAME_TYPE) {
        return writeCNAMERecord(o, rr);
    } else if (rr->type == MX_TYPE) {
        return writeMXRecord(o, rr);
    }

    return 0;
}

unsigned int writeARecord(char* o, dns_rr* rr) {
    uint32_t ipAddr = inet_addr(rr->rdata);
    memcpy(o, &ipAddr, rr->data_len);
    return 16;
}

unsigned int writeCNAMERecord(char* o, dns_rr* rr) {
    char* ini = o;
    uint8_t count = 0;
    int i = 0;
    int j = 1;
    int tempts = 0;
    o++;

    while(1) {
        if (rr->rdata[i] == '.') {
            memcpy(o-count-1, &count, sizeof(char));
            count = 0;
            o++;
            i++;
            tempts = 1;
        } else if (rr->rdata[i] == '\0') {
            memcpy(o, &(rr->rdata[i]), sizeof(char));
            memcpy(o-count-1, &count, sizeof(char));
            count = 0;
            break;
        } else {
            memcpy(o, &(rr->rdata[i]), sizeof(char));
            o++;
            i++;
            count++;
        }
    }

    return 12 + rr->data_len + 1;
}

unsigned int writeMXRecord(char* o, dns_rr* rr) {
    char* ini = o;
    uint8_t count = 0;
    int i = 0;
    int j = 1;
    int tempts = 0;
    o++;

    while(1) {
        if (rr->rdata[i] == '.') {
            memcpy(o-count-1, &count, sizeof(char));
            count = 0;
            o++;
            i++;
            tempts = 1;
            break;
        } else if (rr->rdata[i] == '\0') {
            memcpy(o, &(rr->rdata[i]), sizeof(char));
            memcpy(o-count-1, &count, sizeof(char));
            count = 0;
            break;
        } else {
            memcpy(o, &(rr->rdata[i]), sizeof(char));
            o++;
            i++;
            count++;
        }
    }

    o--;
    uint16_t temp = htons(49164);
    memcpy(o, &temp, sizeof(short));
    return 16 + i;
}