Question

Normally making a copy of a struct is as simple as just using the = operator and the compiler generates code to copy the struct over for you. However, for this part the function has to return a pointer to a struct so I’ve been working with that the whole time only to get to a part where I realized that everything I tried wasn’t copying the struct over correctly.

A basic example of my problem is

typedef struct command_stream *command_stream_t;
command_stream_t ty = (command_stream_t) malloc(sizeof(struct command_stream));
command_stream_t yy;

do some code
//ty contains a variable words which is an array of strings

*yy = *ty;
 ty->words = NULL; //set to null to see if yy still contains a copy of the struct
 printf("%s", yy->words[0]);

I get a segmentation fault here. However, if I change it so it isn’t a pointer

typedef struct command_stream command_stream_t

yy=ty;
ty.words = NULL;
printf("%s", yy.words[0]);

This works just fine! I’m not entirely sure how I should do the same thing for pointers, and I don’t really want to go back and change 500+ codes of lines…

Answer 1

Your yy pointer is never initialized.

You should allocate enough memory there to hold the struct and then either copy with * like you did, or use memcpy with the pointers and size.