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What is the best way to initialize the string array in c?

I tried following two things 

char arr[10] = "\0";
char arr1[10] = {"\0"};

After initializing those string, I tried to display in gdb, both gave the same initialization format. 

(gdb) p arr
$1 = "\000\000\000\000\000\000\000\000\000"
(gdb) p arr1
$2 = "\000\000\000\000\000\000\000\000\000"
(gdb)

I like to know which is best and what are the advantage and disadvantages.

Code:-

int main(){
    char arr[10] = "\0";
    char arr1[10] = {"\0"};

return 0;
}

Assembly:-

(gdb) disass main
Dump of assembler code for function main:

0x00000000004004ec <+0>:    push   %rbp
0x00000000004004ed <+1>:    mov    %rsp,%rbp
0x00000000004004f0 <+4>:    movzwl 0xd5(%rip),%eax        # 0x4005cc
0x00000000004004f7 <+11>:   mov    %ax,-0x10(%rbp)
0x00000000004004fb <+15>:   movq   $0x0,-0xe(%rbp)
0x0000000000400503 <+23>:   movzwl 0xc2(%rip),%eax        # 0x4005cc
0x000000000040050a <+30>:   mov    %ax,-0x20(%rbp)
0x000000000040050e <+34>:   movq   $0x0,-0x1e(%rbp)
0x0000000000400516 <+42>:   mov    $0x0,%eax
0x000000000040051b <+47>:   pop    %rbp
0x000000000040051c <+48>:   retq
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6
  • 1
    Correct me if I'm wrong, but AFAIK they're equivalent. Commented Mar 5, 2013 at 10:50
  • did you compare the disassembly , and see any difference at that level ? Commented Mar 5, 2013 at 10:50
  • @BarathBushan I am not good at assembly. Let me post my assembly code as well. Commented Mar 5, 2013 at 10:55
  • That is not string array, that is char array, also known as "string" in C. String array is a bit vague in C, but usually it means array of char pointers, like argv argument of main function: char *argv[] Commented Mar 5, 2013 at 11:06
  • Also, in C, literal string "" includes terminating '\0' char, in other words, in C empty string is char array with length 1, containing just byte 0. So "\0" is actually a char array of length 2, both 0 (string length is still 0). Commented Mar 5, 2013 at 11:09

4 Answers 4

Reset to default
7

Both initializations are completely equivalent. From the standard:

An array of character type may be initialized by a character string literal or UTF−8 string literal, optionally enclosed in braces.

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1 Comment

@Bingo: yes. I like to call {0} the "universal zero-initializer". It works for everything.
3

Your two initializations are equivalent.

Apart from what you had shown there are several ways which a string (not only [] array) can be initialized:

// fixed size, depending on the lenght of the string, no memory "wasted"
char arr1[] = "value";

// fixed array size, depends on a given number, some memory may be unused
char arr2[10] = "value";

// C-array type initialiation
char arr3[] = {'v','a','l','u','e','\0'};

// special string, should never be modified, need not be freed
char* str1 = "value";

// a dynamic string based on a constant value; has to be freed, but can be reallocated at will
char* str2 = strdup("value");
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3 Comments

Of course it would! noone seems to do it though and I wanted to stress that it should not be modified even without const
strdup() is not described by the C Standard (it is POSIX though). Maybe better to malloc() and strcpy().
maybe it is (though I can't imagine life withouth strdup), but then it's quite long and unintuitive; strdup does it all. If you don't have it, you'll want to implement it anyway.
1

char arr[10] = "\0"; and char arr1[10] = {"\0"}; are equal.

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Comments

1

The statements

char arr[10] = "\0";

and

char arr1[10] = {"\0"};

are exactly the same.

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