遍历和修改C json字符串 [英] Traversing through and modifying a C json string

问题描述

在C中遍历和修改JSON字符串的正确方法是什么?

What's the correct way to traverse and modify a JSON string in C?

具体来说，我有一个字符串，body_buf.打印时

Specifically, I have a string, body_buf. When printed out

print("length: %d\n%.*s\n", body_len, body_len, body_buf);

它看起来像这样:

length: 113
{"field1":"something","whatever":10,"description":"body","id":"random","__oh__":{"session":"12345678jhgfdrtyui"}}

另一个更复杂的body_buf可能看起来像这样:

Another more complicated body_buf may look like this:

{"status":1,"query":{},"proc":{"memory":{"total":17177939968,"cmax":18363625472,"amax":20000000000},"cpu":{"cores":[0.788,0.132,0.319,2.951,10.111,3.309,1.43,0.8,2.705,4.203,2.32,2,0.019,0.172,0.247,3.888,0.282,0.423,5.254,0.258,0.009,0.369,3.277,0.048,0.283,7.574,3.086,1.592,0.191,0.166,4.348,0.391,0.085,0.25,7.12,4.927,3.671,1.147,3.216,4.628,0.131,0.995,0.744,4.252,4.022,3.505,3.758,3.491],"total":108.886,"limit":800},"disk":{"used":20170,"limit":50000,"io_limit":500}}}

我想根据以下规则简化body_buf(它还可以删除敏感信息)，仅修改值，而不修改任何键:

I want to simplify body_buf (which also doubles as removing sensitive information) according to the following rules, only modifying the values, not any of the keys:

1. 字符串成为字符串的长度.
2. 字符串数组变为[array_len，max_len，min_len].
3. 数字数组变为[array_len，max，min].

我不熟悉在C语言中使用JSON字符串的方法.最好的方法是什么?

I'm not familiar with working with JSON strings in C. What's the best way to do this?

我可以将body_buf视作一个字符串并遍历它，修改在:"之后的内容，因为根据类型的不同，这些值必然是我可能要修改的值.对于数组，我需要跟踪夹在"[]"之间的任何内容.和]".这可能有效，但看起来并不简单.

I can treat body_buf as a string and traverse through it, modifying whatever comes after a ":", because those are bound to be the values I might modify, depending on the type. For arrays, I need to keep track of anything that are sandwiched between "[" and "]". This could work but doesn't seem very straightforward.

或者，将body_buf转换为JSON类型，然后遍历嵌套结构.但是然后我也必须对其进行修改.我尚未找到使用json-c或其他方式遍历和修改(或通过某种深层复制创建一个新的)JSON对象的C示例(这将有所帮助).

Alternatively, perhaps convert the body_buf to a JSON type and then traverse through the nested structure. But then I also have to modify it. I have yet to find a C example (which would be helpful) using json-c or otherwise that traverses and modifies (or create a new one via some kind of deep copy?) a JSON object.

除了细节(上面的规则1-3)之外，这应该是一个相对常见的操作-遍历和修改.因此，对于那些更熟悉C语言中json-c或JSON操作的复杂性和良好/标准做法的人，我正在寻找一些指针.

Details (rules above, 1-3) aside, this should be a relatively common operation -- to traverse and modify. So for those more attuned to the intricacies and good/standard practices of json-c or JSON manipulation in general in C, I'm looking for some pointers.

同样，我有json-c:

Again, I have json-c:

#include "cJSON.h"
#include "cJSON_Utils.h"
#include <libjson/json.h>
#include <libjson/json_tokener.h>

到目前为止，我查看的相关信息包括:

Relevant information I've looked at so far include the following:

https://gist.github.com/alan-mushi/19546a0e2c6bd4e059fd

如何在json_tokener_parse()之后获取json值?

使用json-c解析深度嵌套的JSON密钥

推荐答案

我不知道如何简化" json会很有用. 第一次在c中使用json可能会令人恐惧.

I don't know how "simplify" the json will be useful. Using json in c can be scary the first time.

我喜欢cJSON库，它轻便，可移植且稳定. 它具有良好的测试覆盖率，并且许可证是MIT.

I like cJSON library, it is light, portable and stable. It has a good test coverage, and the license is MIT.

我认为使用库cJSON的这段代码将满足您的要求:

I think this code using the library cJSON will do what you asked:

#include <cjson/cJSON.h>
#include <stdbool.h>
#include <string.h>
#include <stdio.h>
#include <limits.h>
#include <float.h>

const char json1[] = "{\"field1\":\"something\",\"whatever\":10,\"description\":\"body\",\"id\":\"random\",\"__oh__\":{\"session\":\"12345678jhgfdrtyui\"}}";
const char json2[] = "{\"status\":1,\"query\":{},\"proc\":{\"memory\":{\"total\":17177939968,\"cmax\":18363625472,\"amax\":20000000000},\"cpu\":{\"cores\":[0.788,0.132,0.319,2.951,10.111,3.309,1.43,0.8,2.705,4.203,2.32,2,0.019,0.172,0.247,3.888,0.282,0.423,5.254,0.258,0.009,0.369,3.277,0.048,0.283,7.574,3.086,1.592,0.191,0.166,4.348,0.391,0.085,0.25,7.12,4.927,3.671,1.147,3.216,4.628,0.131,0.995,0.744,4.252,4.022,3.505,3.758,3.491],\"total\":108.886,\"limit\":800},\"disk\":{\"used\":20170,\"limit\":50000,\"io_limit\":500}}}";
const char json3[] = "{\"Name\":\"Tom\",\"Age\":18,\"Address\":\"California\",\"arr\":[1,2,3,4,5]}";

static void simplifyArray(cJSON *input, cJSON *output)
{  
    cJSON *item;
    size_t noElems = 0;
    
    if (cJSON_IsString(cJSON_GetArrayItem(input, 0))) {
        size_t max, min;
        max = 0;
        min = UINT_MAX;
        cJSON_ArrayForEach(item, input) {
            noElems++;
            size_t len = strlen(cJSON_GetStringValue(item));
            if (len > max) max = len;
            if (len < min) min = len;
        }
        cJSON *newArray = cJSON_AddArrayToObject(output, input->string);
        cJSON_AddItemToArray(newArray, cJSON_CreateNumber(noElems));
        cJSON_AddItemToArray(newArray, cJSON_CreateNumber(max));
        cJSON_AddItemToArray(newArray, cJSON_CreateNumber(min));

    } else if (cJSON_IsNumber(cJSON_GetArrayItem(input, 0))) {
        double max, min;
        max = -DBL_MAX;
        min = DBL_MAX;
        cJSON_ArrayForEach(item, input) {
            noElems++;
            double value = item->valuedouble;
            if (value > max) max = value;
            if (value < min) min = value;
        }
        cJSON *newArray = cJSON_AddArrayToObject(output, input->string);
        cJSON_AddItemToArray(newArray, cJSON_CreateNumber(noElems));
        cJSON_AddItemToArray(newArray, cJSON_CreateNumber(max));
        cJSON_AddItemToArray(newArray, cJSON_CreateNumber(min));
    }
}

static void simplify(cJSON *input, cJSON *output)
{
    cJSON *elem;
    for (elem = input; elem != NULL; elem = elem->next) {
        if (cJSON_IsString(elem)) {
            cJSON_AddNumberToObject(output, elem->string, strlen(cJSON_GetStringValue(elem)));
        } else if (cJSON_IsArray(elem)) {
            simplifyArray(elem, output);
        } else if (cJSON_IsObject(elem)) {
            cJSON *newOutput = cJSON_AddObjectToObject(output, elem->string);
            simplify(elem->child, newOutput);
        } else {
            cJSON *dup = cJSON_Duplicate(elem, true);
            cJSON_AddItemToObject(output, elem->string, dup);
        }
    }
}

static void simplifyAndPrint(const char *json)
{
    cJSON *input = cJSON_Parse(json);
    cJSON *output = cJSON_CreateObject();
    simplify(input->child, output);
    printf("%s\n", cJSON_PrintUnformatted(output));
    cJSON_Delete(input);
    cJSON_Delete(output);
}

int main()
{
    simplifyAndPrint(json1);
    simplifyAndPrint(json2);
    simplifyAndPrint(json3);
    return 0;
}

输出:

{"field1":9,"whatever":10,"description":4,"id":6,"__oh__":{"session":18}}
{"status":1,"query":{},"proc":{"memory":{"total":17177939968,"cmax":18363625472,"amax":20000000000},"cpu":{"cores":[48,10.111,0.009],"total":108.886,"limit":800},"disk":{"used":20170,"limit":50000,"io_limit":500}}}
{"Name":3,"Age":18,"Address":10,"arr":[5,5,1]}

在上面的示例中，我希望不要更改输入JSON，如果您对此不关心，则可以使用功能cJSON_ReplaceItemInObject来替换节点.

In the example above I preferred don't alter the input JSON, if you don't care about this you can use the funcion cJSON_ReplaceItemInObject to substitute the node.

P.S .:我假设数组仅包含字符串和数字，并且不要混合使用，因为没有规则可以处理其他数组配置.

P.S.: I am assuming arrays contain only strings and numbers, and don't mix it, because there is no rule to handle other array configurations.

P.S.2:此代码使用的是Ubuntu 20.04中提供的库版本，如果您从GitHub下载库，则该版本将包含更多功能.

P.S.2: This code is using the version of the library present in Ubuntu 20.04, if you download the library from GitHub the version will contain more features.

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