Re: Persisting a structure: Valgrind errors

Juha Nieminen <nospam@thanks.invalid>
05 Jun 2011 05:57:13 GMT
Ramon <> wrote:

Though I have a good amount of experience in ANSI C, Java, C#...etc, I
am fairly new with C++.

What I am trying to do is to persist a struct to a binary file. The
structure is being saved correctly yet when I am trying to load it from
disk to memory Valgrind is popping up some errors (Invalid write and
Invalid free) from this line of code:*) i, sizeof(struct record));

  Suppose you had this:

struct record
    char* name;
    char* surname;

  Would you expect to be able to save and load the contents of that struct
with a simple fwrite() and fread()? If you did that, you would just have
the pointers pointing to garbage (and if you are lucky you will get a
segmentation fault, but if you aren't, your program will just misbehave
in wild ways).

  If you don't expect it to work in C, why would you expect it to work
in C++? Just because the pointers are wrapped into classes (in this case
std::string) doesn't make it any safer to use raw byte writes and reads.

  Unfortunately C++ does not have automatic serialization features like
many other languages do.

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