set member of array to zero

Question

Morning, I hope somebody is here suppose I have the following structure or even better an array of structures

struct foo {
  int a;
  char b[10];
  char c;
};

struct foo* bar;
bar = (struct foo*) malloc(sizeof(struct foo)*10);
memset(bar, -1, sizeof(struct foo)*10);

instead of

for (counter = 0; counter < 10; ++counter)
      memset(bar[counter],0,sizeof(char)*10);

how to a set b member to 0 in all array of char / b member in all array?

basically my question is a bit similar to this one

You seem to be coding in C. Make your life easier and use C++, e.g. `std::vector`. Then you won't have to play any `malloc` and `memset` shenanigans. — juanchopanza, Dec 05 '16 at 22:37
If you use C, then use `calloc()`, it's like `malloc()` but takes care of the math to determine the right size and it zeroes the memory for you. — G. Sliepen, Dec 05 '16 at 23:10

score 1 · Answer 1 · answered Dec 05 '16 at 23:08

1

I'd like to suggest that rather than using a C-style array of int b[10]; that you use std::array<char,10> b; instead.

Then you can fill it with zeros this way: b.fill(0);. If you need to pass the address of the storage to a C-style function you can do that using b.data(). And of course, you can still access its content using b[i], but if you want more safety, use b.at(i).

http://en.cppreference.com/w/cpp/container/array

answered Dec 05 '16 at 23:08

IanM_Matrix1

1,564
10
8

thank you, but i actually i am looking to get it done in c style – Iurie Cojocari Dec 06 '16 at 22:05
@IurieCojocari Then why did you tag your question C++ and not C? – Lundin Dec 07 '16 at 08:46
i was a my typo, but both solution is good. Thank you for spending time to read and to answer – Iurie Cojocari Dec 07 '16 at 19:49

user253751 · Accepted Answer · 2016-12-05T22:44:55.603

0

You can set the b member of each array element to zero by setting the b member of each array element to zero. You were almost there, but:

You only wanted to zero the b member.
The thing you're zeroing isn't 8 bytes long.

for (counter = 0; counter < 10; ++counter)
    memset(bar[counter].b, 0, sizeof bar[counter].b);

edited Dec 05 '16 at 22:44

answered Dec 05 '16 at 22:31

user253751

57,427
7
48
90

yes I want to set only .b to different value. So I am looking for faster way like just they did – Iurie Cojocari Dec 05 '16 at 22:36
but is there a method by using offset to initialise all .b without any for loop – Iurie Cojocari Dec 05 '16 at 22:46
It might be answer that then we use memset we specify the range of memory which should be clear out to a given value so that it might corrupt entire memory – Iurie Cojocari Dec 05 '16 at 22:55
@IurieCojocari No. – user253751 Dec 05 '16 at 22:55
Sorry for pouting, does it mean it might be possible to solve this problem by memset(bar, 0, offsetOfb + structureAndress)? – Iurie Cojocari Dec 05 '16 at 23:03
@IurieCojocari No. – user253751 Dec 05 '16 at 23:28

set member of array to zero

2 Answers2