离开 function 后结构变量值发生更改

Question

I am struggled to write a correct title for the post. Forgive me if it is not 100% accurate. Because, the initial issue was just freeing a malloc ed output without disturbing where it is assigned to. I then decided to copy the source ( encrypt_Data ) into another variable before I free it. And then another issue arose this time. It is where I am. If I can find a proper solution at least for one of them it would be great.

Issue#1

 typedef struct {
      const char*             sTopic;
      const char*             pData;
    } CLIENT_MESSAGE;
CLIENT_MESSAGE Publish;

char * pData = "Hello World!";
char * encrypt_Data = Encrypt_Data_Base64(pData);
Publish.pData = encrypt_Data;
free(encrypt_Data);

If I free the encrypt_Data , Publish.pData is also freed (as they are just a pointer and pointing to the same memory location). Note that: The function Encrypt_Data_Base64 has several several nested function called underneath and it has malloc ed output. This is why I try to free the memory sourced from there.

And then I decided to make a copy of the encrypt_Data so I can then free it freely.

Issue#1 solving attempt

char * pData = "Hello World!";
char * encrypt_Data = Encrypt_Data_Base64(pData);
// ------- addition starts ------
int len = strlen(encrypt_Data);
char temp[len+1];
char * pTemp = temp;
memcpy(pTemp, encrypt_Data, len+1);
pTemp[len] = '\0';
// ------- addition ends------
Publish.pData = pTemp
free(encrypt_Data);

Struct variable value preserved well. So far so good. And then I have to pass the struct to a library function (I don't have source code for it).

Issue#2

CLIENT_Publish(&Publish); // This is how it supposed to be.
//Prototype: int CLIENT_Publish(CLIENT_MESSAGE* pPublish);

And this time, when I debug, as soon as my current function is left and just called that one before doing anything else, the struct value has been altered. I assumed this might be related to non-terminated string. I therefore added NUL termination as you may see in the solving attempt above. But it didn't help.

Array content before leaving the function (required block is between 0 and 12)

Array content when entering the other function (CLIENT_Publish)

Since I can't do much about the library part, I have to do something in the part I can control.

EDIT: If I get my value without using this line char * encrypt_Data = Encrypt_Data_Base64(pData);

for example;

AFunction_GetPtr(&pData);
Publish.pData = pData;
CLIENT_Publish(&Publish);

This way, it works nice and easy. But, I like to intercept the value coming from the AFunction_GetPtr and use it in Encrypt_Data_Base64 and then pass it to CLIENT_Publish .

Any input highly appreciated.

Answer 1

It is not the correct solution, but the simplest thing for you to do right now is:

char * pData = "Hello World!";
char * encrypt_Data = Encrypt_Data_Base64(pData);
Publish.pData = strdup(encrypt_Data);
free(encrypt_Data);

Now that you've made another copy of the data, you'll need to eventually free it. So you might as well just do:

char * pData = "Hello World!";
char * encrypt_Data = Encrypt_Data_Base64(pData);
Publish.pData = encrypt_Data;
/* Do not free(encrypt_Data); */

Just remember to free Publish.pData when you no longer need it.