Question

I have a function that parse a JSON text and return a new structure called EZapiEntry.
When I check the value of result every thing is OK.

After using this function in an athor c file. I get wrong results.

Code of the function:

EZapiEntry parseEntry()
 {
    EZapiEntry   result;
    json_t      *entryJson;
    entryJson = json_object_get(root,"data");
    unsigned int i=0;
    EZuc8* maskString=json_string_value(json_object_get(entryJson,"mask"));
    result.uiKeySize = json_integer_value(json_object_get(entryJson,"keySize"));
    result.uiResultSize = json_integer_value(json_object_get(entryJson,"resultSize"));
    EZuc8 val1[result.uiKeySize];   
    hexStringToBytes(json_string_value(json_object_get(entryJson,"key")),val1);
    result.pucKey = val1;   
    EZuc8 val2[result.uiResultSize];
    hexStringToBytes(json_string_value(json_object_get(entryJson,"result")),val2);  
    result.pucResult = val2;
    EZuc8 val3[strlen(maskString)];
    hexStringToBytes(maskString,val3);  
    result.pucMask = val3;
    result.uiProfile = json_integer_value(json_object_get(entryJson,"profile"));
        printf("\nkeySize :  %u  ",result.uiKeySize);
        printf("\nResultSize :  %u  ",result.uiResultSize);
        printf("\nkey :    ");
        for (i = 0 ; i <result.uiKeySize ; i++)
        {
            printf("%02x",result.pucKey[i]);
        }
        printf("\nresult :    ");
        for (i = 0 ; i <result.uiResultSize ; i++)
        {
           printf("%02x",result.pucResult[i]);
        }
        printf("\nmask :    ");
        for (i = 0 ; i <strlen(maskString) ; i++)
        {
          printf("%02x",result.pucMask[i]);
         }  
        printf("\nprofile :    ");
        printf("%u",result.uiProfile);  
    return result;
 }

code of the use of the function :

 entry=parseEntry();
   printf("\nkeySize2 :  %u  ",entry.uiKeySize);
   printf("\nResultSize2:  %u  ",entry.uiResultSize);
   printf("\nkey2 :    ");
    for (i = 0 ; i <entry.uiKeySize ; i++)
    {
       printf("%02x",entry.pucKey[i]);
    }
   printf("\nresult2 :    ");
    for (i = 0 ; i <entry.uiResultSize ; i++)
    {
       printf("%02x",entry.pucResult[i]);
    }
   printf("\nprofile2 :    ");
   printf("%u",entry.uiProfile);

And this is the result :

keySize :  1  
ResultSize :  16  
key :    03
result :    aaaaaa11445544ff00112233445544ff
mask :    0000000a
profile :    0
keySize2 :  1  
ResultSize2:  16  
key2 :    bf
result2 :    bfb985b0102e765c00112233445544ff
profile2 :    0

The first values for example Result1 is the correct one. The second is the wrong one

I am really stack, i can’t find the problem !
Is there any Help ?

Answer 1

This will result in a dangling pointer after the function returns:

EZuc8 val2[result.uiResultSize];
hexStringToBytes(json_string_value(json_object_get(entryJson,"result")),val2);  
result.pucResult = val2;

as val2 will no longer exist when parseEntry() returns. Similar problem for val1 and val3. Instead of using VLA malloc() directly to the relevant member:

result.pucResult = malloc(sizeof(EZuc8) * result.uiResultSize);
hexStringToBytes(json_string_value(json_object_get(entryJson,"result")),
                 result.pucResult);

Remember to free() the dynamically allocated memory.