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Help with C character vs C string


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wide_usa

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Joined: 31 Jan 2024
Posts: 1
Location: USA

PostPosted: Thu May 09, 2024 1:37 am
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I was programming in mainframe C does anyone know why if I use memcpy(str,',',1) it fills 1 byte of str with a NULL. If I do memcpy(str,",",1) it'll add a comma instead.
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Joerg.Findeisen

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Joined: 15 Aug 2015
Posts: 1281
Location: Bamberg, Germany

PostPosted: Thu May 09, 2024 1:48 am
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Code:
Declaration: void *memcpy(void *, const void *, size_t);

Strings in C are defined by "", means your "," IS in fact a comma. WAD.

Quote:
The "char" type in C represents a single character, and the "*" symbol indicates that it is a pointer to a character. A pointer is a type of variable that stores the memory address of another variable. So, "(char *)" is used to cast a value to a pointer to a character type.

Garbage In, Garbage Out someone used to say. icon_wink.gif
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sergeyken

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Joined: 29 Apr 2008
Posts: 2051
Location: USA

PostPosted: Thu May 09, 2024 3:14 am
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wide_usa wrote:
I was programming in mainframe C does anyone know why if I use memcpy(str,',',1) it fills 1 byte of str with a NULL. If I do memcpy(str,",",1) it'll add a comma instead.

The statement
Code:
 memcpy( str, ',', 1 )
MUST give you a compilation error, because the type of argument number 2 (e.g. char) does not match the required type of parameter number 2, as per the function definition (e.g. const char *)

The level of your question proves to me that you’ve heard about C language for the first time only two, or maximum three days ago.

Please, try to learn something.
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Joerg.Findeisen

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Joined: 15 Aug 2015
Posts: 1281
Location: Bamberg, Germany

PostPosted: Thu May 09, 2024 11:36 am
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sergeyken wrote:
The statement
Code:
 memcpy( str, ',', 1 )
MUST give you a compilation error, because the type of argument number 2 (e.g. char) does not match the required type of parameter number 2, as per the function definition (e.g. const char *)

It does of course

Code:
A parameter of type "const void *" cannot be initialized with an expression of type "char".
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