Pass values to a struct

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Good afternoon.

I am in doubt whether it is possible to pass values to a C struct using JSON, Hibernate or some other known method?

c struct

  • Pointer Reaf/write (like char*) is typically nontextual. and you’re writing a memory address... Writing and reading pointers, could only work within the same process (within the same session)

  • What is the purpose? Otherwise the answer will be too broad.

  • I want to pass the values I collect from the database to a C struct

  • So for the record - this is called "serialization" (in this case, to read back, "deserialization")

  • You noticed that there is no "automated" way to do this - you had to create a mini-protocol for serialization - in your case, mark the string and integer fields with a special character. There are thousands of different serialization protocols in the world - and depending on the application, it may be worth adopting a more standardized one, so that other programs can understand your data.

1 answer

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Oh guys, I managed to solve the problem, I’ll leave the code in case someone needs one of these days

#include <stdio.h>
#include <malloc.h>
#include <string.h>

typedef struct __attribute__((__packed__)){
    char *s;
    int *x;
}my_struct;

void *chr2struct(const char *text){
    char c;
    my_struct *mst = (my_struct *) malloc(sizeof(my_struct));
    void **swap = (void **) malloc(sizeof(my_struct));
    void **res = swap;

    if(!text)
        return 0;

    int i;
    while(*text){
        c = *text;
        text++;
        char str[32];
        int x, len;
        char *data;
        switch(c){
            case 's':
            case 'c':
                sscanf(text,"%[^\037]",str);
                text += strlen(str)+1;
                len = atoi(str);
                data = (void *) malloc(sizeof(char)*len);
                strcpy(data,text);
                text+= len+1;
                swap[i] = data;
                break;
            case 'i':
                sscanf(text,"%[^\037]",str);
                text += strlen(str)+1;
                len = atoi(str);
                data = (void *) malloc(sizeof(int)*len);
                for(x=0; x<len; x++){
                    sscanf(text,"%i",&data[x]);
                    sprintf(str,"%i",data[x]);
                    text+=strlen(str)+1;
                    swap[i] = *data;
                }
                break;
            default:
                return 0;
        }
        i++;
    }

    return res;
}

int main(int argc, char *argv[]){
    my_struct *mst;
    mst = (my_struct *) chr2struct("s16\037qwertyuiopasdfgh\0i1\03716\0");
    printf("%s | %i\n", mst->s, mst->x);
}

  • If you are learning C, I advise you to use a C compiler instead of a C++ compiler. Learning C using a C++ compiler is like learning Swedish with a Danish teacher.

  • Turn on all your compiler warnings and pay attention to warnings!

  • I program directly from the linux terminal, I don’t use ide, as for the compiler I use gcc even, and the warnings, only had one in sscanf that reads an integer, but at the moment I don’t intend to create an entire variable to receive the integer values.

  • Hmmm, I didn’t notice the <malloc.h>. Anyway you must prefer the <stdlib.h> (that I noticed does not exist in the code) and fail to make the conversation to the value returned by malloc().

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