Nested structure to char array

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hi i am trying to convert the nested structure to char array using sprintf function in c programming.

struct date_of_birth{
	int dd,mm,yy;
};

struct student{
	char name[30];
	int rollNumber;
	date_of_birth dob;
};
int main()
{
// to make a single char aray using sprintf()
char arr[100];
  
}

What I have tried:

can you please let me which loop will continue first either student or dob to form char array?

Posted 8-Aug-17 10:10am

bijaynayak

Updated 8-Aug-17 11:12am

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[no name] 8-Aug-17 20:59pm

Do you want to be able to reverse the process - turn the char array back to struct?

2 solutions

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CPallini · Answer 1 · 2017-08-08T11:12:00

Solution 2

If you need to serialize[^] the struct then memcpy[^] is the way to go

C++

student s;
char a[100];
memcpy(a, &s, sizeof(s));

[update]Fixed a blunder, thanks to K5054[/update].

Posted 8-Aug-17 11:12am

CPallini

Updated 8-Aug-17 20:29pm

v2

Comments

k5054 8-Aug-17 18:58pm

That should be memcpy(a, &s, sizeof s)

Note that sizeof only needs brackets if its operand is a type rather than a variable.

It should also be pointed out that in this case the contents of a[] are not human readable.

CPallini 9-Aug-17 2:33am

Thanks for pointing out the blunder.
I know about sizeof. It could be just a matter of style, anyway I prefer using the unnecessary brackets.
Serialized data could be (and in fact often are) not human readable.

bijaynayak 10-Aug-17 2:53am

hi thanks for the suggestion, but according to my requirement ,
1:i need to transfer the strut data to multiple servers (or we can say diff nodes
) & that server understand only char.
2:memcpy is not suggestible because it work with address, from receiving end how to get the same structure data

CPallini 10-Aug-17 3:03am

'memcpy is not suggestible because it work with address, from receiving end how to get the same structure data'
This is the very purpose of serialization/deserialization. Did you check out the Wikipedia page I linked?

[no name] 9-Aug-17 2:27am

Maybe:

student s;
char a[sizeof s];
memcpy(a, &s, sizeof s)

Rick York · Answer 2 · 2017-08-08T10:41:00

Solution 1

One way :

C++

void GetStudentDataString( student * ps )
{
   const int bufferSize = 127;
   char buffer[bufferSize+1] = {0};

   snprintf( buffer, bufferSize, "%s, %d, %02d:%02d:%02d",
             ps->name, ps->rollNumber, ps->yy, ps->mm, ps->dd );
}

Posted 8-Aug-17 10:41am

Rick York

Comments

k5054 8-Aug-17 18:47pm

Couple of notes

snprintf writes at most size bytes, including the terminating null byte to the destination, so you don't need to manually account for it.

you forgot to include the dob member when printing the date of birth. So we end up with the following:

snprintf(buffer, sizeof buffer, "%s, %d, %02d:%02d:%02d",       ps->name, ps->rollNumber, ps->dob.yy, ps->dob.mm, ps->dob.dd);

[no name] 8-Aug-17 21:00pm

The OP did not specify whether they wished to deserialise in which case this would not work.

bijaynayak 9-Aug-17 1:58am

hi pwasser, yes need to deserialise the char [] to again struct.

[no name] 9-Aug-17 2:20am

OK then why not use use memcpy() to copy struct to array and memcpy() to copy from array back to struct?

Rick York 9-Aug-17 11:30am

The OP asked for sprintf to be used.

[no name] 9-Aug-17 20:19pm

OK but how will you deserialise back to struct?

bijaynayak 10-Aug-17 2:47am

Hi pwasser,
i will keep all struct members in to a : separated value after that i will
split this with strtok()which will split the above buffer.

sample code below:
struct student studt2;

snprintf(buffer,bufferSize,"%s:%d:%d:%d:%d",studt.name,studt.rollNumber,studt.dob.dd,studt.dob.mm,studt.dob.yy);
ptr = strtok(buffer,":");

while(ptr != NULL)
{
// studt2.name= strtok(buffer);
strcpy(studt2.name,strtok(buffer));
studt2.rollNumber=atoi(ptr);
ptr=strtok(NULL,":");
}
but how to store values of respective members again ?
problem is basicaly with studt2.name...

[no name] 10-Aug-17 4:02am

Why go this way? It is not a good solution. memcpy() solves all this neatly.

Rick York 11-Aug-17 20:09pm

I have written strtok parsing loops so many times I have lost count. Here's a typical example of one :

const size_t MaxTokens = 64; // maximum number of tokens expected
char * tokens[MaxTokens] = {0};
const char * delimiters = "\t,;:.";
char * tokenString = buffer; // text string to parse for tokens
size_t count = 0;
while( strtok( tokenString, &tokens[count] ) && ( count < maxTokens ) )
{
tokenString = nullptr;
++count;
}

// examine the tokens here