背景：先用wireshark抓数据帧，过滤自己需要的之后转换为json文件，然后使用jsoncpp工具解析，获取其中有用的数据，最后把数据写入到文件中，之后分析数据或根据数据画图。
我分析的json文件格式如下，是抓取的usb数据，我需要的是"usb.capdata"键值的数据，由于"23:80:45:80"是两个数据，并且是小端格式，这个数据应该是0823h和0845h，所以我我还需要做一些转换

{"_index": "packets-2024-04-23","_type": "doc","_score": null,"_source": {"layers": {"frame": {"frame.section_number": "1","frame.interface_id": "0","frame.interface_id_tree": {"frame.interface_name": "\\\\.\\USBPcap1","frame.interface_description": "USBPcap1"},"frame.encap_type": "152","frame.time": "Apr 23, 2024 17:07:55.755688000 中国标准时间","frame.offset_shift": "0.000000000","frame.time_epoch": "1713863275.755688000","frame.time_delta": "0.000135000","frame.time_delta_displayed": "0.000000000","frame.time_relative": "41.255565000","frame.number": "25","frame.len": "31","frame.cap_len": "31","frame.marked": "0","frame.ignored": "0","frame.protocols": "usb"},"usb": {"usb.src": "1.12.1","usb.addr": "1.12.1","usb.dst": "host","usb.addr": "host","usb.usbpcap_header_len": "27","usb.irp_id": "0xffff9503afc4da20","usb.usbd_status": "0x00000000","usb.function": "0x0009","usb.irp_info": "0x01","usb.irp_info_tree": {"usb.irp_info.reserved": "0x00","usb.irp_info.direction": "0x01"},"usb.bus_id": "1","usb.device_address": "12","usb.endpoint_address": "0x81","usb.endpoint_address_tree": {"usb.endpoint_address.direction": "1","usb.endpoint_address.number": "1"},"usb.transfer_type": "0x03","usb.data_len": "4","usb.request_in": "23","usb.time": "0.000229000","usb.bInterfaceClass": "0x0a"},"usb.capdata": "23:80:45:80"}}}

代码如下

#include "json/json.h"
#include <fstream>
#include <iostream>
/*** $g++ readFromStream.cpp -ljsoncpp -std=c++11 -o readFromStream* $./readFromStream*/void readFileJson();
int main(int argc, char* argv[]) {readFileJson();return EXIT_SUCCESS;
}void readFileJson() {Json::Reader reader;Json::Value root;string ifilename, ofilename;cout << "please input json file name:";cin >> ifilename;cout << "please input output file name:";cin >> ofilename;cout << "start~" << endl;//从文件中读取，保证当前文件有json文件ifstream in(ifilename, ios::binary);if (!in.is_open()) {cout << "Error opening file\n";return;}if (reader.parse(in, root)) {string usb_capdata;	//usb原数据ofstream rf;		//数据输出句柄const char* c1; // string转换数组原数据char c2[5];     //截取翻转之后数据int num;        //转换为十进制int strsize = root.size();	//一个数据帧是一组数据，这个也表示有多少个数据帧rf.open(ofilename, ios::binary);	//如果没有文件则创建for (int i = 0; i < strsize; i++) {usb_capdata = root[i]["_source"]["layers"]["usb.capdata"].asString();c1 = usb_capdata.c_str(); //string转换为char型//23:80:45:80//第一个数据c2[0] = c1[3];c2[1] = c1[4];c2[2] = c1[0];c2[3] = c1[1];c2[4] = '\0';num = strtol(c2, NULL, 16); //转换为十进制rf << num << ","; //写入文件//第二个数据c2[0] = c1[9];c2[1] = c1[10];c2[2] = c1[6];c2[3] = c1[7];c2[4] = '\0';num = strtol(c2, NULL, 16);rf << num << endl;}rf.close(); //关闭数据输出文件cout << "Reading Complete!" << endl;} else {cout << "parse error\n" << endl;}in.close(); //关闭数据输入文件system("pause");
}