copying members of structure to another structure

Question

i'm trying to copy members from one structure to another structure, but i have no clue how to do so.

struct StudentTxt
{
    int ID;
    string lname;
    string fname;
    string initial;
    int age;
    double balance;
};
struct StudentBin
{
    int ID;
    int age;
    double balance;
    char fullname[50];
};

i read the file and store all the data into the first structure, and after that i combined the lname, fname,initial into one string.

the question is i'm trying to copy the string to the fullname in the second structure, and also the ID, age, Balance.

can someone guide me to the right path.

any help will be appreciated.

You're converting from one structure to another. The problem has nothing to do with anything special about *your* structures. *Write code* that builds the structure content you *want* from the structure content you *have*. You have tried that, right? Certainly so. *Post what you have tried so far*. — WhozCraig, Apr 30 '14 at 17:58

score 2 · Answer 1 · answered Apr 30 '14 at 17:56

2

How about writing a function to perform the translate and copy?

void studentCopy( StudentTxt const * pSrc, StudentBin * pDst ) {
    pDst->ID = pSrc->ID;
    pDst->age= pSrc->age;
    pDst->balance = pSrc->balance;

    string const name = pSrc->fname + pSrc->initial + pSrc->lname;
    size_t const dstLen = sizeof( pDst->fullname );
    strncpy( & pDst->fullname, name.c_str(), dstLen );
    pDst->fullname[ dstLen - 1 ] = 0;    // NUL terminate
}

answered Apr 30 '14 at 17:56

Arun

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thanks, can you explain what does -> mean in your code. – user3080461 Apr 30 '14 at 18:06
1

+1 for being the only answer that actually saw the general problem. The opening sentence "How about writing a function to perform the translate and copy" on its own would have earned my uptick, as it is the correct solution. Adding an *implementation* is just exceeding the bar. – WhozCraig Apr 30 '14 at 18:10
@user3080461: '->' is pointer dereference. `pSrc` is a pointer to a `StudentTxt` object. `pSrc->ID` returns the `ID` value of that referred object. See http://stackoverflow.com/questions/4955198/what-does-dereferencing-a-pointer-mean for further details. – Arun Apr 30 '14 at 19:37

Rakib · Answer 2 · 2014-04-30T18:01:46.440

1

u can just declare fullname as std::string and then write fullname= lname+ " "+fname+" "+initial; while converting.

if u have to use char array then do the following:

           strcat(fullname,lname.c_str());
           strcat(fullname,fname.c_str());
           strcat(fullname,initial.c_str());

remember to initialize fullname by fullname[0]=0; before the above operations. you can also use strcat(fullname," "); after each concatenation for proper format.

And then simply copy other attributes of the first structure into the second.

edited Apr 30 '14 at 18:01

answered Apr 30 '14 at 17:53

Rakib

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i can't, the full name should stay as a C_string. – user3080461 Apr 30 '14 at 17:54
In absence of any length checks, such series of `strcat()` may overflow the destination buffer, `fullname`. – Arun Apr 30 '14 at 19:38

score 1 · Answer 3 · answered Apr 30 '14 at 17:54

1

Why can't you just use the assignment operator?

// Say these are for the same student
StudentTxt studentATxt;
StudentBin studentABin;

// Copy items over
StudentABin.ID = StudentATxt.ID;
StudentABin.age = StudentATxt.age;
StudentBin.fullname = StudentTxt.fname.c_str()

...etc

answered Apr 30 '14 at 17:54

Cory Kramer

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thanks, but i have 15 different line of data that i need to store in StudentBin structure array. – user3080461 Apr 30 '14 at 17:57
@user3080461 Yes.... so put this assignment logic into a function. That is the purpose of functions, so you can re-use code. – Cory Kramer Apr 30 '14 at 17:58
1

The last line isn't even valid code. You can't use an array as an lvalue in an assignment. – WhozCraig Apr 30 '14 at 18:02

PeterSW · Answer 4 · 2014-04-30T19:51:42.787

1

For the fullname part:

std::string fullname(
    StudentATxt.lname + " " +
    StudentATxt.fname + " " +
    StudentATxt.initial);

if(fullname.size() < 50)
    strcpy(StudentABin.fullname, fullname.c_str());

edited Apr 30 '14 at 19:51

answered Apr 30 '14 at 17:58

PeterSW

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`StudentABin.fullname = fullname.c_str();` is a pointer assignment. It becomes invalid as soon as the (stack) object `fullname` goes out of scope. To avoid that, the contents of string need to be copied. – Arun Apr 30 '14 at 19:41
Hi @Arun thanks for pointing that out! I've corrected the answer now... – PeterSW Apr 30 '14 at 19:52

copying members of structure to another structure

4 Answers4