CODEWITHSUNDEEP
cfile-io
Jim Newtron
Jim Newtron

Reputation: 227

Struct Array passed as parameter to read() issue

I have a struct defined as

struct my_struct {
    struct hdr_str hdr;
    char *content; 
};

I am trying to pass the content in my_struct of the first element in my_struct by nesting it all as a parameter to read()

what I have is

struct my_struct[5];

read is defined as 

ssize_t read(int fd, void *buf, size_t count);

and I am trying to pass it as

read(fd, my_struct[0].content, count)

But I am receiving -1 as a return value, with errno = EFAULT (bad address)

Any idea how to make read read into a char * in a struct array?

Upvotes: 0

Views: 71

Answers (1)

simonc
simonc

Reputation: 42215

You'll need to allocate memory for read to copy data into.

If you know the maximum size of data you'll read, you could change my_struct to

struct my_struct {
    struct hdr_str hdr;
    char content[MAX_CONTENT_LENGTH]; 
};

where MAX_CONTENT_LENGTH is #define'd by you to your known max length.

Alternatively, allocate my_struct.content on demand once you know how many bytes to read

my_struct.content = malloc(count);
read(fd, my_struct[0].content, count);

If you do this, make sure to later use free on my_struct.content to return its memory to the system.

Upvotes: 2

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