【Linux c/c++ 实现json文件动态修改】

- 此代码实现了，一个动态映射表，类似于键值对，通过key作为索引点，实现增删改等功能。

1.json库使用

此源码使用cJSON库，cJosn官方源码地址

https://sourceforge.net/projects/cjson/

2.json文件生成

2.1.初始化json数据类型，实现了一个特征值数组与对应id映射表

static int init_map_file()
{
    cJSON *root,*featuresArr;
    cJSON * feature_list[MAX_FEATURE_NUMBER];
    root = cJSON_CreateObject();
    featuresArr = cJSON_CreateArray();
    cJSON *feature_tmp = NULL;
    //填充特征值数组
    for(int i = 0;i<MAX_FEATURE_NUMBER;i++)
    {
        feature_list[i] = cJSON_CreateObject();
        feature_tmp = feature_list[i];
        cJSON_AddNumberToObject(feature_tmp, GID_ITEM,INVALID_GID);
        cJSON_AddNumberToObject(feature_tmp, DID_ITEM,INVALID_DB_ID);
        cJSON_AddNumberToObject(feature_tmp, STATUS_ITEM,FFS_ST_EMPTY);
        cJSON_AddItemToArray(featuresArr, feature_tmp);
    }
    cJSON_AddItemToObject(root, FEATURELISTS_ITEM, featuresArr);
    create_json_map_file(root);
    cJSON_Delete(root);
    return 0;
}

2.2.将json数据格式，生成对应的json文件

static int create_json_map_file(cJSON *root)
{
    char* buf = cJSON_Print(root);
    printf("buf:%s\n",buf);
    FILE* fp = fopen(MAPPING_TABLE_FILE,"w");
    if(NULL != fp)
    {
        fwrite(buf,strlen(buf),1,fp);
        fclose(fp);
    }
    else{
        printf("Failed to open %s...",MAPPING_TABLE_FILE);
    }
    free(buf);
    return 0;
}

3.json文件解析

3.1.json文件大小获取

static size_t get_file_size(const char *filepath)
{
    /*check input para*/
    if(NULL == filepath)
        return 0;
    struct stat filestat;
    memset(&filestat,0,sizeof(struct stat));
    /*get file information*/
    if(0 == stat(filepath,&filestat))
        return filestat.st_size;
    else
        return 0;
}

3.2.json文件读出到内存

static char *read_file_to_buf(const char *filepath)
{
    /*check input para*/
    if(NULL == filepath)
    {
        return NULL;
    }
    /*get file size*/
    size_t size = get_file_size(filepath);
    if(0 == size)
        return NULL;
        
    /*malloc memory*/
    char *buf = (char*)malloc(size+1);
    if(NULL == buf)
        return NULL;
    memset(buf,0,size+1);
    
    /*read string from file*/
    FILE *fp = fopen(filepath,"r");
    size_t readSize = fread(buf,1,size,fp);
    if(readSize != size)
    {
        /*read error*/
        free(buf);
        buf = NULL;
        return NULL;
    }

    buf[size] = 0;
    return buf;
}

3.3.读取内存文件到cjson对象

static cJSON *prepare_parse_json(const char *filePath)
{
    /*check input para*/
    if(NULL == filePath)
    {
        printf("input para is NULL\n");
        return NULL;
    }
    /*read file content to buffer*/
    char *buf = read_file_to_buf(filePath);
    if(NULL == buf)
    {
        printf("read file to buf failed\n");
        return NULL;
    }
    /*parse JSON*/
    cJSON *pTemp = cJSON_Parse(buf);
    free(buf);
    buf = NULL;
    return pTemp;
}

4.json文件更新

4.1.增加特征值

int json_add_feature(int gid,int db_id)
{
    if(0 != access(MAPPING_TABLE_FILE,0))
    {
        init_map_file();
    }
    bool isAddSuccess = false;
    int featureSts = FFS_ST_IDEL;
    cJSON *root = NULL;
    root = prepare_parse_json(MAPPING_TABLE_FILE);
    cJSON* featuresArr = NULL;
    featuresArr = cJSON_GetObjectItem(root,FEATURELISTS_ITEM);
    //获取数组大小
    int arrLen = cJSON_GetArraySize(featuresArr);
    cJSON * arrNumEle = NULL;
    for (int i = 0; i < arrLen; i++)
    {
        //获取数组元素item
        arrNumEle = cJSON_GetArrayItem(featuresArr, i);
        if(NULL == arrNumEle)
        {
            continue;
        }
        featureSts = cJSON_GetObjectItem(arrNumEle, STATUS_ITEM)->valueint;
        if(FFS_ST_EMPTY == featureSts) 
        {
            //设置gid
            cJSON_GetObjectItem(arrNumEle,GID_ITEM)->valueint = gid;
            cJSON_GetObjectItem(arrNumEle,GID_ITEM)->valuedouble = gid;

            //设置db_id
            cJSON_GetObjectItem(arrNumEle,DID_ITEM)->valueint = db_id;
            cJSON_GetObjectItem(arrNumEle,DID_ITEM)->valuedouble = db_id;

            //设置块储存状态
            cJSON_GetObjectItem(arrNumEle,STATUS_ITEM)->valueint = FFS_ST_FILLED;
            cJSON_GetObjectItem(arrNumEle,STATUS_ITEM)->valuedouble = FFS_ST_FILLED;
            isAddSuccess = true;
            break;
        }
        else{
            continue;
        }
    }
    create_json_map_file(root);
    cJSON_Delete(root);
    sync();
    if(isAddSuccess)
    {
        return 0;
    }
    else{
        return -1;
    }
}

4.2.删除特征值

int json_delete_feature(int gid)
{
    bool isDeleteSuccess = false;
    int tmp_gid = INVALID_GID;
    cJSON *root = NULL;
    root = prepare_parse_json(MAPPING_TABLE_FILE);
    cJSON* featuresArr = NULL;
    featuresArr = cJSON_GetObjectItem(root,FEATURELISTS_ITEM);
    //获取数组大小
    int arrLen = cJSON_GetArraySize(featuresArr);
    cJSON * arrNumEle = NULL;
    for (int i = 0; i < arrLen; i++)
    {
        //获取数组元素item
        arrNumEle = cJSON_GetArrayItem(featuresArr, i);
        if(NULL == arrNumEle)
        {
            continue;
        }
        tmp_gid = cJSON_GetObjectItem(arrNumEle, GID_ITEM)->valueint;
        if(gid != tmp_gid) 
        {
            continue;
        }
        else{
            cJSON_GetObjectItem(arrNumEle,GID_ITEM)->valueint = INVALID_GID;
            cJSON_GetObjectItem(arrNumEle,GID_ITEM)->valuedouble = INVALID_GID;
            cJSON_GetObjectItem(arrNumEle,DID_ITEM)->valueint = INVALID_DB_ID;
            cJSON_GetObjectItem(arrNumEle,DID_ITEM)->valuedouble = INVALID_DB_ID;
            cJSON_GetObjectItem(arrNumEle,STATUS_ITEM)->valueint = FFS_ST_EMPTY;
            cJSON_GetObjectItem(arrNumEle,STATUS_ITEM)->valuedouble = FFS_ST_EMPTY;
            isDeleteSuccess = true;
            break;
        }
    }
    create_json_map_file(root);
    cJSON_Delete(root);
    sync();
    if(isDeleteSuccess)
    {
        return 0;
    }
    else{
        return -1;
    }
}

5.源码测试及源文件

5.1main.cpp测试此源码

#include <stdio.h>
#include "common.h"
int main()
{
    json_add_feature(123,656423);
    json_add_feature(456,5805213);
    json_delete_feature(456);
    json_add_feature(673,85353);
    return 0;
}

5.2 json原始文件，初始化map

5.3 main.cpp执行打印如下

5.4 common.cpp源码如下

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/time.h>
#include <sys/stat.h>
#include "cjson.h"
#include "common.h"

static size_t get_file_size(const char *filepath)
{
    /*check input para*/
    if(NULL == filepath)
        return 0;
    struct stat filestat;
    memset(&filestat,0,sizeof(struct stat));
    /*get file information*/
    if(0 == stat(filepath,&filestat))
        return filestat.st_size;
    else
        return 0;
}

static char *read_file_to_buf(const char *filepath)
{
    /*check input para*/
    if(NULL == filepath)
    {
        return NULL;
    }
    /*get file size*/
    size_t size = get_file_size(filepath);
    if(0 == size)
        return NULL;
        
    /*malloc memory*/
    char *buf = (char*)malloc(size+1);
    if(NULL == buf)
        return NULL;
    memset(buf,0,size+1);
    
    /*read string from file*/
    FILE *fp = fopen(filepath,"r");
    size_t readSize = fread(buf,1,size,fp);
    if(readSize != size)
    {
        /*read error*/
        free(buf);
        buf = NULL;
        return NULL;
    }

    buf[size] = 0;
    return buf;
}

static cJSON *prepare_parse_json(const char *filePath)
{
    /*check input para*/
    if(NULL == filePath)
    {
        printf("input para is NULL\n");
        return NULL;
    }
    /*read file content to buffer*/
    char *buf = read_file_to_buf(filePath);
    if(NULL == buf)
    {
        printf("read file to buf failed\n");
        return NULL;
    }
    /*parse JSON*/
    cJSON *pTemp = cJSON_Parse(buf);
    free(buf);
    buf = NULL;
    return pTemp;
}

static int create_json_map_file(cJSON *root)
{
    char* buf = cJSON_Print(root);
    printf("buf:%s\n",buf);
    FILE* fp = fopen(MAPPING_TABLE_FILE,"w");
    if(NULL != fp)
    {
        fwrite(buf,strlen(buf),1,fp);
        fclose(fp);
    }
    else{
        printf("Failed to open %s...",MAPPING_TABLE_FILE);
    }
    free(buf);
    return 0;
}

static int init_map_file()
{
    cJSON *root,*featuresArr;
    cJSON * feature_list[MAX_FEATURE_NUMBER];
    root = cJSON_CreateObject();
    featuresArr = cJSON_CreateArray();
    cJSON *feature_tmp = NULL;
    //填充特征值数组
    for(int i = 0;i<MAX_FEATURE_NUMBER;i++)
    {
        feature_list[i] = cJSON_CreateObject();
        feature_tmp = feature_list[i];
        cJSON_AddNumberToObject(feature_tmp, GID_ITEM,INVALID_GID);
        cJSON_AddNumberToObject(feature_tmp, DID_ITEM,INVALID_DB_ID);
        cJSON_AddNumberToObject(feature_tmp, STATUS_ITEM,FFS_ST_EMPTY);
        cJSON_AddItemToArray(featuresArr, feature_tmp);
    }
    cJSON_AddItemToObject(root, FEATURELISTS_ITEM, featuresArr);
    create_json_map_file(root);
    cJSON_Delete(root);
    return 0;
}

int json_delete_feature(int gid)
{
    bool isDeleteSuccess = false;
    int tmp_gid = INVALID_GID;
    cJSON *root = NULL;
    root = prepare_parse_json(MAPPING_TABLE_FILE);
    cJSON* featuresArr = NULL;
    featuresArr = cJSON_GetObjectItem(root,FEATURELISTS_ITEM);
    //获取数组大小
    int arrLen = cJSON_GetArraySize(featuresArr);
    cJSON * arrNumEle = NULL;
    for (int i = 0; i < arrLen; i++)
    {
        //获取数组元素item
        arrNumEle = cJSON_GetArrayItem(featuresArr, i);
        if(NULL == arrNumEle)
        {
            continue;
        }
        tmp_gid = cJSON_GetObjectItem(arrNumEle, GID_ITEM)->valueint;
        if(gid != tmp_gid) 
        {
            continue;
        }
        else{
            cJSON_GetObjectItem(arrNumEle,GID_ITEM)->valueint = INVALID_GID;
            cJSON_GetObjectItem(arrNumEle,GID_ITEM)->valuedouble = INVALID_GID;
            cJSON_GetObjectItem(arrNumEle,DID_ITEM)->valueint = INVALID_DB_ID;
            cJSON_GetObjectItem(arrNumEle,DID_ITEM)->valuedouble = INVALID_DB_ID;
            cJSON_GetObjectItem(arrNumEle,STATUS_ITEM)->valueint = FFS_ST_EMPTY;
            cJSON_GetObjectItem(arrNumEle,STATUS_ITEM)->valuedouble = FFS_ST_EMPTY;
            isDeleteSuccess = true;
            break;
        }
    }
    create_json_map_file(root);
    cJSON_Delete(root);
    sync();
    if(isDeleteSuccess)
    {
        return 0;
    }
    else{
        return -1;
    }
}

int json_add_feature(int gid,int db_id)
{
    if(0 != access(MAPPING_TABLE_FILE,0))
    {
        init_map_file();
    }
    bool isAddSuccess = false;
    int featureSts = FFS_ST_IDEL;
    cJSON *root = NULL;
    root = prepare_parse_json(MAPPING_TABLE_FILE);
    cJSON* featuresArr = NULL;
    featuresArr = cJSON_GetObjectItem(root,FEATURELISTS_ITEM);
    //获取数组大小
    int arrLen = cJSON_GetArraySize(featuresArr);
    cJSON * arrNumEle = NULL;
    for (int i = 0; i < arrLen; i++)
    {
        //获取数组元素item
        arrNumEle = cJSON_GetArrayItem(featuresArr, i);
        if(NULL == arrNumEle)
        {
            continue;
        }
        featureSts = cJSON_GetObjectItem(arrNumEle, STATUS_ITEM)->valueint;
        if(FFS_ST_EMPTY == featureSts) 
        {
            //设置gid
            cJSON_GetObjectItem(arrNumEle,GID_ITEM)->valueint = gid;
            cJSON_GetObjectItem(arrNumEle,GID_ITEM)->valuedouble = gid;

            //设置db_id
            cJSON_GetObjectItem(arrNumEle,DID_ITEM)->valueint = db_id;
            cJSON_GetObjectItem(arrNumEle,DID_ITEM)->valuedouble = db_id;

            //设置块储存状态
            cJSON_GetObjectItem(arrNumEle,STATUS_ITEM)->valueint = FFS_ST_FILLED;
            cJSON_GetObjectItem(arrNumEle,STATUS_ITEM)->valuedouble = FFS_ST_FILLED;
            isAddSuccess = true;
            break;
        }
        else{
            continue;
        }
    }
    create_json_map_file(root);
    cJSON_Delete(root);
    sync();
    if(isAddSuccess)
    {
        return 0;
    }
    else{
        return -1;
    }
}

5.5 common.h 源码如下

#ifndef __COMMON_H__

#define __COMMON_H__
#define MAPPING_TABLE_FILE "feature_map.json"
#define MAX_FEATURE_NUMBER  (6)

typedef enum tagFeature_STORE_STATUS{
    FFS_ST_IDEL = -1,
    FFS_ST_EMPTY,
    FFS_ST_FILLED
}FSS_ST;

#define INVALID_GID                       (0xff)
#define INVALID_DB_ID                     (0xff)
#define FEATURELISTS_ITEM                 "featureLists" //储存映射表数组名称
#define GID_ITEM                          "gid"          //极氪指定的gid
#define DID_ITEM                          "did"          //算法返回的特征值db_id
#define STATUS_ITEM                       "status"       //预分配块映射表存储状态

int json_add_feature(int gid,int db_id);
int json_delete_feature(int gid);
#endif