Question

I have the following code

struct Info { int age; char name[5]; }
char buffer[20];
Info i;
i.age = 10;
sprintf(i.name, "Case");
strncpy(buffer+5, (char*)&i, sizeof(Info));

Now I want to recover the record

Info j;
strncpy((char*)&j, buffer+5, sizeof(Info));
printf("%d %s", j.age, j.name);

However this prints empty string for name. I’m not sure what I am doing wrong.

Answer 1

There are two problems with your copying mechanism:

1. You’re assuming that sizeof(Info) is 5. That’s definitely not the case.
2. You’re using strncpy, which is for strings. Info is not a string, so you need to use memcpy.

The following will work:

char buffer[sizeof(i)];
memcpy(buffer, &i, sizeof(i));

...

memcpy(&j, buffer, sizeof(j));

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There’s also another problem; name[5] is not big enough to hold "Casey", as that’s 6 characters once you’ve accounted for the null terminator.