How to initialize string in struct without using strcpy function?

Question

Is there any manual way to initialize the string in struct ? I used to initialize string in struct using strcpy function such as:

typedef struct {
    int id;
    char name[20];
    int age;
} employee;


int main()
{
    employee x;
    x.age=25;

    strcpy(x.name,"sam");
    printf("employee age is %d \n",x.age);
    printf("employee name is %s",x.name);

    return 0;
}

to copy into a fixed-size array, you should always use strncpy(), or strncpy_s, if available. — Michaël Roy, Aug 20 '17 at 00:12
@MichaëlRoy Disagree with "to copy into a fixed-size array, you should always use strncpy(), ..." — chux - Reinstate Monica, Aug 20 '17 at 03:29
You can. But don't come posting questions here about buffer overflow. — Michaël Roy, Aug 20 '17 at 03:31

Vlad from Moscow · Accepted Answer · 2017-08-20T00:20:44.583

7

Strictly speaking this

strcpy(x.name,"sam");

is not an initialization.

if to speak about the initialization then you can do it the following way

employee x = { .name = "sam", .age = 25 };

or

employee x = { .name = { "sam" }, .age = 25 };

This is equivalent to the following initialization

employee x = { 0, "sam", 25 };

or

employee x = { 0, { "sam" }, 25 };

Or you even can use a compound literal of the type employee to initialize the object x though that is not efficient.

Otherwise if is not an initialization but an assignment of the data member of the structure then indeed you have to use at least strcpy or strncpy.

edited Aug 20 '17 at 00:20

answered Aug 19 '17 at 23:46

Vlad from Moscow

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Good answer aside from "compound literal ... though that is not efficient.". Certainly a good compiler will optimize that as well as other approaches. – chux - Reinstate Monica Aug 20 '17 at 03:23
Assignment can use a _compound literal_ without `strcpy()` and friends. – chux - Reinstate Monica Aug 20 '17 at 03:27

lost_in_the_source · Answer 2 · 2017-08-20T12:25:26.120

-1

You can write your own version of strcpy:

void mycopy(char *dest, const char *source, size_t ndest)
{
    assert(ndest != 0);
    while (--ndest > 0 && (*dest++ = *source++))
        ;
}

You're not using strcpy anymore. Plus it is safer.

edited Aug 20 '17 at 12:25

answered Aug 19 '17 at 23:37

lost_in_the_source

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You should have clearly marked this as "sarcastic". I assume it is sarcastic. If not, then your employer should be frightened. – gnasher729 Aug 19 '17 at 23:49
@gnasher729 why should my boss my scared? This version is safer – lost_in_the_source Aug 19 '17 at 23:50
1

I have not seen so badly written simple function for years – 0___________ Aug 19 '17 at 23:56
@PeterJ Where are the problems? – lost_in_the_source Aug 19 '17 at 23:57
@PeterJ, that's the user's fault for passing bad input. I could add an assertion, but i didnt want to distract – lost_in_the_source Aug 20 '17 at 00:01
3

going to bed enough for today – 0___________ Aug 20 '17 at 00:05
1

There need to be parentheses around the assignment since `&&` has higher precedence than `=`. – ad absurdum Aug 20 '17 at 00:10
1

Your function is as safe as strncpy, If the string is longer than max, the destination is not null terminated. strncpy_s was added to the library so we shouldn't have to squint at code like this. – Michaël Roy Aug 20 '17 at 00:17
Thinking about it, your function is slower than strncpy() for the exact same functionality, and dangers. – Michaël Roy Aug 20 '17 at 00:21
2

Corner case weakness: `mycopy(dest, source, 0)` leads to buffer overrun. `strncpy()` does not have that problem. – chux - Reinstate Monica Aug 20 '17 at 03:25

0___________ · Answer 3 · 2017-08-20T08:36:12.897

-1

max - including trailing zero

char *mystrncpy(char *dest, const char *src, size_t max)
{
    char *tmp = dest;

    if (max)
    {
        while (--max && *src)
        {
            *dest++ = *src++;
        }

    *dest++ = '\0';
    }
    return tmp;
}

edited Aug 20 '17 at 08:36

answered Aug 19 '17 at 23:59

0___________

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`*dest++ = '\0';` belongs inside `if(max)` – chux - Reinstate Monica Aug 20 '17 at 03:24

How to initialize string in struct without using strcpy function?

3 Answers3