Declaration of a character array in C - Clash between Norminette and Compiler-CodePudding

I am hoping somebody could please clarify what I am doing wrong. I am trying to replicate the strcpy function in C.

The exercise requires us to create two loop through a src string and replace the content at each corresponding index at the destination string. My issue is when I create the test function in int main() I initialise a character array and assign it some content. It compiles fine however I get a norminette error:

// Method 1

char    str1[5] = "abcde";// Error: DECL_ASSIGN_LINE   Declaration and assignation on a single line

char    str2[5] = "fghij"; //Error: DECL_ASSIGN_LINE Declaration and assignation on a single line

If I initialise and assign like bellow, Norminette is ok but I get a compilation error:

// Method 2

char    str1[5] = "abcde";

char    str2[5] = "fghij"; 


str1[] = "abcde"; // error: expected expression before ‘]’ token ... (with an arrow pointing to ] bracket) 

str2[] = "fghij"; // error: expected expression before ‘]’ token ... (with an arrow pointing to ] bracket)

// Method 3

char    str1[] = {'a', 'b', 'c', 'd', 'e','\0'}; // Error: DECL_ASSIGN_LINE   Declaration and assignation on a single line

char    str2[] = {'f', 'g', 'h', 'i', 'j', '\0'};//Error: DECL_ASSIGN_LINE Declaration and assignation on a single line

I have also tried various methods including str[5] = "abcde" after declaration with no success. My question is how can I declare these character arrays to satisfy both the norminette and compiler?

Also is my understand that in C, a character array and a string are interchangeable concepts? Thank you

CodePudding user response：

In method 2:

str1[] = "abcde"; // error:

is an assignment, so it's invalid. The [] syntax can only be used in a definition. More on this below.

Method 3 is fine. Whoever is flagging this is wrong.

In method 1 [and other places]:

char str1[5] = "abcde";

is wrong because it should be:

char str1[6] = "abcde";

to account for the EOS (0x00) string terminator at the end.

An alternate would be:

char str1[] = "abcde";

And, you did this [more or less] in method 3:

char str1[] = {'a', 'b', 'c', 'd', 'e', '\0'};

AFAICT, this was flagged by the external tool (not the compiler?). It is a perfectly valid alternative.

CodePudding user response：

Also is my understand that in C, a character array and a string are interchangeable concepts?

No. In C, a string is a sequence of character values including a 0-valued terminator. The string "abcde" would be represented by the sequence {'a', 'b', 'c', 'd', 'e', 0}. That terminator is how the various string handling routines like strlen and strcpy know where the end of the string is.

Strings (including string literals like "abcde") are stored in arrays of character type, but not every array of character type stores a string - it could be a character sequence with no 0-valued terminator, or it could be a character sequence including multiple 0-valued bytes.

In order to store a string of N characters, the array has to be at least N 1 elements wide:

char str1[6] = "abcde";  // 5 printing characters plus 0 terminator
char str1[6] = "fghij";

You can declare the array without an explicit size, and the size (including the 1 for the terminator) will be determined from the size of the initializer:

char str1[] = "abcde"; // will allocate 6 elements for str1
char str2[] = "fghij";

I've found the documentation for Norminette and ... ugh.

I get that your school wants everyone to follow a common coding standard; that makes it easier to analyze and grade everyone's code. But some of its rules are just plain weird and non-idiomatic and, ironically, encourage bad style. If I'm interpreting it correctly, it wants you to write your initializers as

char str1[] 
  = "abcde";

or something equally bizarre. Nobody does that.

One way to get around the problem is to not initialize the array in the declaration, but assign it separately using strcpy:

char str1[6]; // size is required since we don't have an initializer
char str2[6];

strcpy( str1, "abcde" );
strcpy( str2, "fghij" );

You cannot use = to assign whole arrays outside of a declaration (initialization is not the same thing as assignment). IOW, you can't write something like

str1 = "abcde";

as a statement.

You either have to use a library function like strcpy or strncpy (for strings) or memcpy (for things that aren't strings), or you have to assign each element individually:

str1[0] = 'a';
str1[1] = 'b';
str1[2] = 'c';
...