怎么用C语言获取JSON中的数据？

用C语言获取JSON中的数据的方法是使用 CJSON。

以下简单介绍用CJSON的思路及实现：

1）创建json，从json中获取数据虚祥庆。

#nclude <stdio.h>

#include "cJSON.h"

char * makeJson()

{

cJSON * pJsonRoot = NULL

pJsonRoot = cJSON_CreateObject()

if(NULL == pJsonRoot)

{

//error happend here

return NULL

}

cJSON_AddStringToObject(pJsonRoot, "hello", "hello world")

cJSON_AddNumberToObject(pJsonRoot, "number", 10010)

cJSON_AddBoolToObject(pJsonRoot, "bool", 1)

cJSON * pSubJson = NULL

pSubJson = cJSON_CreateObject()

if(NULL == pSubJson)

{

// create object faild, exit

cJSON_Delete(pJsonRoot)

return NULL

}

cJSON_AddStringToObject(pSubJson, "subjsonobj", "a sub json string")

cJSON_AddItemToObject(pJsonRoot, "subobj", pSubJson)

char * p = cJSON_Print(pJsonRoot)

// else use :

// char * p = cJSON_PrintUnformatted(pJsonRoot)

if(NULL == p)

{

//convert json list to string faild, exit

//because sub json pSubJson han been add to pJsonRoot, so just delete pJsonRoot, if you also delete pSubJson, it will coredump, and error is : double free

cJSON_Delete(pJsonRoot)

return NULL

}

//free(p)

cJSON_Delete(pJsonRoot)

return p

}

void parseJson(char * pMsg)

{

if(NULL == pMsg)

{

return

}

cJSON * pJson = cJSON_Parse(pMsg)；

if(NULL == pJson)

{

// parse faild, return

return

}

// get string from json

cJSON * pSub = cJSON_GetObjectItem(pJson, "hello")

if(NULL == pSub)

{

//get object named "hello" faild

}

printf("obj_1 : %s\n", pSub->宴纤valuestring)

// get number from json

pSub = cJSON_GetObjectItem(pJson, "number")

if(NULL == pSub)

{

//get number from json faild

}

printf("obj_2 : %d\n", pSub->valueint)

// get bool from json

pSub = cJSON_GetObjectItem(pJson, "bool")

if(NULL == pSub)

{

// get bool from json faild

}

printf("obj_3 : %d\n", pSub->valueint)

// get sub object

pSub = cJSON_GetObjectItem(pJson, "差握subobj")

if(NULL == pSub)

{

// get sub object faild

}

cJSON * pSubSub = cJSON_GetObjectItem(pSub, "subjsonobj")

if(NULL == pSubSub)

{

// get object from subject object faild

}

printf("sub_obj_1 : %s\n", pSubSub->valuestring)

cJSON_Delete(pJson)

}

int main()

{

char * p = makeJson()

if(NULL == p)

{

return 0

}

printf("%s\n", p)

parseJson(p)

free(p)//这里不要忘记释放内存，cJSON_Print()函数或者cJSON_PrintUnformatted（）产生的内存，使用free(char *)进行释放

return 0

}

2）创建json数组和解析json数组

//创建数组，数组值是另一个JSON的item，这里使用数字作为演示

char * makeArray(int iSize)

{

cJSON * root = cJSON_CreateArray()

if(NULL == root)

{

printf("create json array faild\n")

return NULL

}

int i = 0

for(i = 0i <iSizei++)

{

cJSON_AddNumberToObject(root, "hehe", i)

}

char * out = cJSON_Print(root)

cJSON_Delete(root)

return out

}

//解析刚刚的CJSON数组

void parseArray(char * pJson)

{

if(NULL == pJson)

{

return

}

cJSON * root = NULL

if((root = cJSON_Parse(pJson)) == NULL)

{

return

}

int iSize = cJSON_GetArraySize(root)

for(int iCnt = 0iCnt <iSizeiCnt++)

{

cJSON * pSub = cJSON_GetArrayItem(root, iCnt)

if(NULL == pSub)

{

continue

}

int iValue = pSub->valueint

printf("value[%2d] : [%d]\n", iCnt, iValue)

}

cJSON_Delete(root)

return

}

有两种方法：

一是标准的输出输入方式 比如新建一个磁盘文件c:\a.txt， 将键盘输入的一字符串写到文件中：

FILE *ft

char str[50]

ft=fopen("c:\\a.txt","w+")

printf("输入一个字符串：")

scanf("%s",str)

fputs(str,ft)

fclose(ft)

//重新打开这个文件并读出字符串，显示在屏幕上 ft=fopen("c:\\a.txt","rt")

fgets(str,50,ft)

fclose(ft)printf("%s",str)

二是低级输入输出方式 仍如上例：

int hdchar str[50]printf("输入一个字符串：")

scanf("%s",str)

hd=open("c:\\a.txt",O_CREAT|O_TEXT|O_WRONLY)

write(hd,str,strlen(str))

close(hd)//重新打开这个文件并读出字符串，显示在屏幕上。

hd=open("c:\\a.txt",O_TEXT|O_RDONLY)read(hd,str,50)

close(hd)printf("%s",str)。

有的圆缺唯是 下面橘培是超市扮亮 请自选 JSON_checker. YAJL. js0n. LibU. json-c. json-parser. jsonsl. WJElement. M's JSON parser. cJSON. Jansson. jsmn. cson. parson. ujson4c. nxjson.

1、读取文件全部内容

#include <stdio.h>

#include <stdlib.h>

int main(int argc, char* argv[])

{

char ch

FILE* fp

unsigned long int count = 0

char buf[1025] = {0}

// 这里要求我们在输入两个参数，第一个为 exe 路径，第二个为 文件名

// 如 file_test.exe test.txt

if (argc != 2)

{

printf("Usage: %s filename\n", argv[0])

exit(EXIT_FAILURE)

}

if ((fp = fopen(argv[1], "r")) == NULL)

{

// 如果文件打开失败（通常是文件不存在），则结束程序

printf("Can't open %s\n", argv[1])

exit(EXIT_FAILURE)

}

while ((ch = getc(fp)) != EOF &&count <1024)

{

// 显示文本内容并计数

buf[count] = ch

count++

}

fclose(fp)

printf("%s\n", buf)

printf("File %s has %lu characters\n", argv[1], count)

return 0

}

2、cJSON解析字符串

编译选项要加 -lm

示例源串

{

"server": {

"nodes": [{

"ip": "10.76.76.190",

"port": 6379

}, {

"ip": "丛哪10.76.76.191",

"port": 6380

}, {

"ip"冲郑卖: "10.76.76.192",

"port": 6381

}],

"password": "admin"

},

"isssl": true

}

登录后复制

示例代码（每一行记得判空，编译时加-lm选项）

#include <stdio.h>

#include "cJSON.h"

int main(){

char c[] = "{\"server\":{\"nodes\":[{\"ip\":\"10.76.76.190\",\"port\":6379},{\"ip\":\"10.76.76.191\",\"port\":6380},{\散逗"ip\":\"10.76.76.192\",\"port\":6381}],\"password\":\"admin\"},\"isssl\":true}"

cJSON* root = cJSON_Parse(c)

cJSON* json_server = cJSON_GetObjectItem(root, "server")

cJSON* json_isssl = cJSON_GetObjectItem(root, "isssl")

cJSON* json_password = cJSON_GetObjectItem(json_server, "password")

cJSON* json_nodes = cJSON_GetObjectItem(json_server, "nodes")

int i = 0

for (i != cJSON_GetArraySize(json_nodes)++i) {

cJSON* each = cJSON_GetArrayItem(json_nodes, i)

cJSON* json_ip = cJSON_GetObjectItem(each, "ip")

cJSON* json_port = cJSON_GetObjectItem(each, "port")

printf("ip %s\n", json_ip->valuestring)

printf("port %d\n", json_port->valueint)

}

printf("password %s\n", json_password->valuestring)

printf("is ssl %s\n", json_isssl->valueint ? "true":"false")

cJSON_Delete(root)

}

3、curl拿到回传的数据

编译选项要加 -lcurl

头部选项参考

https://curl.se/libcurl/c/curl_easy_setopt.html

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <curl/curl.h>

struct string {

char* ptr

size_t len

}

void init_string(struct string* s) {

s->len = 0

s->ptr = malloc(s->len + 1)

if (s->ptr == NULL) {

fprintf(stderr, "malloc() failed\n")

exit(EXIT_FAILURE)

}

s->ptr[0] = '\0'

}

size_t writefunc(void* ptr, size_t size, size_t nmemb, struct string* s) {

size_t new_len = s->len + size * nmemb

s->ptr = realloc(s->ptr, new_len + 1)

if (s->ptr == NULL) {

fprintf(stderr, "realloc() failed\n")

exit(EXIT_FAILURE)

}

memcpy(s->ptr + s->len, ptr, size * nmemb)

s->ptr[new_len] = '\0'

s->len = new_len

return size * nmemb

}

int main(void) {

CURL* curl

CURLcode res

curl = curl_easy_init()

if(curl) {

struct string s

init_string(&s)

curl_easy_setopt(curl, CURLOPT_URL, "https://www.baidu.com")

curl_easy_setopt(curl, CURLOPT_POSTFIELDS, "test")

curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, writefunc)

curl_easy_setopt(curl, CURLOPT_WRITEDATA, &s)

res = curl_easy_perform(curl)

printf("打印数据:\n%s", s.ptr)

free(s.ptr)

/* always cleanup */

curl_easy_cleanup(curl)

}

return 0

}

4、获取随机数

#include <stdio.h>

int main(int argc, char* argv[]){

srand((int)time(0))

//打印 32位 test 随机数，并用16进制表示

int test2 = rand()

printf("%lx \n", test2)

// 打印 64位 test 随机数，并用16进制表示， 016代表不足16位的部分，补零，llx代表打印64位的16进制数

unsigned long long test = ((unsigned long long)rand() <<32) + rand()

printf("%016llx \n", test)

return 0

}

5、定义按位的结构体

总结，按照位定义结构体，一定要都按照位定义，不然会出现意想不到的错误，而且一定要定义无符号的

#include <stdio.h>

#pragma pack (1)

struct test1 {

unsigned char cloud_id:3

unsigned char vendor_id:4

unsigned short machine_id

unsigned long long current_time:41

}

struct test2 {

unsigned char cloud_id:3

unsigned char vendor_id:4

unsigned short machine_id:16

unsigned long long current_time:41

}

int main(int argc, char* argv[]){

printf("test1 大小 : %d \n", sizeof(struct test1))

printf("test2 大小 : %d \n", sizeof(struct test2))

return 0

}

6、按位打印01字节码

#include <stdio.h>

// 修改type后面的类型，可以查看各种数的字节码

#define type unsigned int

void print_bin(type num)

{

int len = sizeof(type)

int n = 8

int i, j, k

unsigned char *p = (unsigned char*)&num + len -1

for (i = 0i <leni++) //处理len个字节

{

j = *(p - i)//取每个字节的首地址

for ( k = 7k >= 0k--) //处理每个字节的8个位

{

if (j &(1 <<k))

printf("1")

else

printf("0")

}

printf(" ")

}

printf("\r\n")

}

int main(int argc, char* argv[]){

type a = 100

print_bin(a)

return 0

}

登录后复制

7、打印16进制字节码

#include<stdio.h>

typedef unsigned char uint8

#define HEXDUMP_LINE_LENGTH 16

void hex_dump(uint8* data, int length)

{

uint8* p = data

int i, line, offset = 0

while (offset <length)

{

printf("%04x ", offset)

line = length - offset

if (line >HEXDUMP_LINE_LENGTH)

line = HEXDUMP_LINE_LENGTH

for (i = 0i <linei++)

printf("%02x ", p[i])

for (i <HEXDUMP_LINE_LENGTHi++)

printf(" ")

for (i = 0i <linei++)

printf("%c", (p[i] >= 0x20 &&p[i] <0x7F) ? p[i] : '.')

printf("\n")

offset += line

p += line

}

}

8、打印字节码简易版

#include <stdio.h>

#include <string.h>

#include <stdlib.h>

void main() {

unsigned char Buf[] = "123456"

unsigned int len = strlen(Buf)

char* Buf1 = (char*)malloc(len * 3 + 1)

int i = 0, k = 0

for (i <len * 3i += 3, k++)

snprintf(&Buf1[i], 4, "%02x ", Buf[k])

printf(Buf1)

free(Buf1)

}

9、逐级创建文件夹

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <sys/stat.h>

#include <sys/types.h>

int mkdir_recursively(char* dir) {

if (NULL == dir)

return 1

size_t len = strlen(dir)

char* str = malloc(len + 1)

if (NULL == str)

return 1

strcpy(str, dir)

int i = 0

for (i = 0i <leni++) {

if (str[i] == '/') {

if (i == 0)

continue

str[i] = '\0'

if (access(str, 0) != 0) {

if (mkdir(str, S_IRWXU | S_IRGRP | S_IXGRP | S_IROTH | S_IXOTH)) {

free(str)

return 1

}

}

str[i] = '/'

}

}

if (len >0 &&access(str, 0) != 0) {

if (mkdir(str, S_IRWXU | S_IRGRP | S_IXGRP | S_IROTH | S_IXOTH)) {

free(str)

return 1

}

}

free(str)

return 0

}

int main() {

mkdir_recursively("/home/test/abc/edf")

---