一、介紹
實際項目參數需要保存；有些配置信息需要存放于文件，這里給出demo示例

二、原理
1、使用文件存儲到文件系統
2、使用json庫進行封裝和解析

三、示例
config_para.c

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include "cJSON.h"
#include <fcntl.h>

const char nConfigFile[] = "configPara.config";

typedef struct{
    char ip[32];
    unsigned short port;
}onenet_http_def;

typedef struct{
    char devId[32];
    char apiKey[128];
    char authentication[128];
    char productId[32];
}onenet_para_def;

typedef struct {
    onenet_http_def onenethttp;
    onenet_para_def dataPoint;
    onenet_para_def gpsPoint;
}config_para_def;

config_para_def config_para = {0};

static config_para_def default_para = {
    .onenethttp.ip = "183.230.40.33",
    .onenethttp.port = 80,
    .dataPoint.devId = "803857251",
    .dataPoint.apiKey = "a=FF2LEzpb0EzX=bO=T46TW4Qes=",
    .dataPoint.productId = "465267",
    .dataPoint.authentication = "guoguo1233211234567",
    .gpsPoint.devId = "803857251",
    .gpsPoint.apiKey = "a=FF2LEzpb0EzX=bO=T46TW4Qes=",
    .gpsPoint.productId = "465267",
    .gpsPoint.authentication = "guoguo1233211234567",
};

char read_buff[2048] = {0};

int checkefileexist(char *filename)
{
    if((access(filename, F_OK)) == -1) 
    {
        printf("%s file not exist %s line:%d\n", filename, __FILE__, __LINE__);
        return (-1);
    }
    return 0;
}

int read_file(char *filename, char *buff, int len)
{
	FILE *fp;
	int ret = 0;
	
	fp = fopen(filename, "r");
	if(fp == NULL)
	{
		printf("打開文%s件失敗\n", filename);
		return (-1);
	}

	ret = fread(buff, 1, len, fp);

	fclose(fp);
	
	return ret;
}

int jsonparse(char *buff, int len)
{
    cJSON *cjson = NULL, *onenethttp_json = NULL, *dataPoint_json = NULL,*gpsPoint_json = NULL;
    char *str_tmp = NULL;
    int int_tmp = 0;

    cjson = cJSON_Parse(buff);//將JSON字符串轉換成JSON結構體
	if(cjson == NULL)						//判斷轉換是否成功
	{
		printf("cjson error...\r\n");
        return (-1);
	}
	else
	{
		printf("%s\n",cJSON_Print(cjson));//打包成功調用cJSON_Print打印輸出
	}
    printf("json parse:\n");
    onenethttp_json = cJSON_GetObjectItem(cjson,"onenethttp");	//解析對象
    str_tmp = cJSON_GetObjectItem(onenethttp_json, "ip")->valuestring;	//解析對象中的字符串
    strcpy(config_para.onenethttp.ip, str_tmp);
    printf("ip:%s\n", str_tmp);
    free(str_tmp);
    int_tmp = cJSON_GetObjectItem(onenethttp_json, "port")->valueint;	//解析對象中的字符串
    config_para.onenethttp.port = int_tmp;
    printf("port:%d\n", int_tmp);

    dataPoint_json = cJSON_GetObjectItem(cjson,"dataPoint");	//解析對象
    str_tmp = cJSON_GetObjectItem(dataPoint_json, "devId")->valuestring;	//解析對象中的字符串
    strcpy(config_para.dataPoint.devId, str_tmp);
    printf("dataPoint devId:%s\n", str_tmp);
    free(str_tmp);
    str_tmp = cJSON_GetObjectItem(dataPoint_json, "apiKey")->valuestring;	//解析對象中的字符串
    strcpy(config_para.dataPoint.apiKey, str_tmp);
    printf("dataPoint apiKey:%s\n", str_tmp);
    free(str_tmp);

    gpsPoint_json = cJSON_GetObjectItem(cjson,"gpsPoint");	//解析對象
    str_tmp = cJSON_GetObjectItem(gpsPoint_json, "devId")->valuestring;	//解析對象中的字符串
    strcpy(config_para.gpsPoint.devId, str_tmp);
    printf("gpsPoint devId:%s\n", str_tmp);
    free(str_tmp);
    str_tmp = cJSON_GetObjectItem(gpsPoint_json, "apiKey")->valuestring;	//解析對象中的字符串
    strcpy(config_para.gpsPoint.apiKey, str_tmp);
    printf("gpsPoint apiKey:%s\n", str_tmp);
    free(str_tmp);
    
    return 0;
}

int read_config()
{
    int ret = 0;

    ret = checkefileexist(nConfigFile);
    if(ret != 0)
    {
        config_para = default_para;
        printf("use default para %s line:%d\n", __FILE__, __LINE__);
    }
    else
    {
        memset(read_buff, 0, 2048);
        ret = read_file(nConfigFile, read_buff, 2048);
        if(ret == -1)
        {
            printf("read file error %s line:%d\n", __FILE__, __LINE__);
            config_para = default_para;
            return (-1);
        }
        else
        {
            printf("len: %d \nfile %s\n", ret, read_buff);
            ret = jsonparse(read_buff, 2048);
            if(ret == -1)
                config_para = default_para;
        }
    }

    return 0;
}

int write_file(char *filename, char *buff, int len)
{
	FILE *fp;
	int ret;
	
	fp = fopen(filename, "w");
	if(fp == NULL)
	{
		printf("打開文%s件失敗\n",filename);
		return 0;
	}

	ret = fwrite(buff, 1, len, fp);
	if(ret != len)
	{
		printf("寫入%s文件失敗",filename);
	}

	fclose(fp);
}

int write_config(config_para_def config_para)
{
    cJSON *config_json = cJSON_CreateObject();				//創建一個對象

    cJSON *onenethttp_json	= cJSON_CreateObject();				//創建一個對象
	cJSON_AddStringToObject(onenethttp_json,"ip", config_para.onenethttp.ip);	//添加字符串 
	cJSON_AddNumberToObject(onenethttp_json,"port", config_para.onenethttp.port);	//添加整型數字
 	cJSON_AddItemToObject(config_json, "onenethttp", onenethttp_json);

    cJSON *dataPoint_json	= cJSON_CreateObject();				//創建一個對象
	cJSON_AddStringToObject(dataPoint_json,"devId", config_para.dataPoint.devId);	//添加字符串 
	cJSON_AddNumberToObject(dataPoint_json,"apiKey", config_para.dataPoint.apiKey);	//添加整型數字
 	cJSON_AddItemToObject(config_json, "onenethttp", dataPoint_json);

    cJSON *gpsPoint_json	= cJSON_CreateObject();				//創建一個對象
	cJSON_AddStringToObject(gpsPoint_json,"devId", config_para.gpsPoint.devId);	//添加字符串 
	cJSON_AddNumberToObject(gpsPoint_json,"apiKey", config_para.gpsPoint.apiKey);	//添加整型數字
 	cJSON_AddItemToObject(config_json, "onenethttp", gpsPoint_json);

    char *json_data = cJSON_Print(config_json);	//JSON數據結構轉換為JSON字符串
	printf("%s\n", json_data);//輸出字符串

    write_file(nConfigFile, json_data, strlen(json_data));
	cJSON_Delete(config_json);//清除結構體
    
    return 0;
}

config_para.h

#ifndef __CONFIG_PARA_H
#define __CONFIG_PARA_H

typedef struct{
    char ip[32];
    unsigned short port;
}onenet_http_def;

typedef struct{
    char devId[32];
    char apiKey[128];
    char authentication[128];
    char productId[32];
}onenet_para_def;

typedef struct {
    onenet_http_def onenethttp;
    onenet_para_def dataPoint;
    onenet_para_def gpsPoint;
}config_para_def;

extern config_para_def config_para;
int read_config();
int write_config(config_para_def config_para);

#endif

configPara.config

{
    "onenethttp": {
        "ip": "183.230.40.33",
        "port": 80
    },
    "dataPoint": {
        "devId": "803857251",
        "apiKey": "a=FF2LEzpb0EzX=bO=T46TW4Qes=",
        "productId": "465267",
        "authentication": "guoguo1233211234567"
    },
    "gpsPoint": {
        "devId": "803857251",
        "apiKey": "a=FF2LEzpb0EzX=bO=T46TW4Qes=",
        "productId": "465267",
        "authentication": "guoguo1233211234567"
    }
}

test.c

#include <stdio.h>
#include "config_para.h"

int main()
{
	read_config();
	return 0;
}

編譯腳本
buildtest.sh

gcc test.c cJSON.c config_para.c -o test -lm

echo "main run..."
./test

編譯

結果