curl - Using #define to a string in C++

Question

While trying to upload an image with cURL, I am confused because of the code below.

#define UPLOAD_FILE_AS  "testImage.jpg"
static const char buf_1 [] = "RNFR " UPLOAD_FILE_AS;

What I want to understand is,

1. exact type of defined UPLOAD_FILE_AS : array of char / string / or something else?
2. exact operation performed in second line : After second line, buf_1 becomes "RNFR testImage.jpg". But second line only have a space between "RNFR" and UPLOAD_FILE_AS. I've never heard a space can replace "+" operator or merging function. How is this possible?

question from:https://stackoverflow.com/questions/65841540/using-define-to-a-string-in-c

Answer 1

1. The definition of the macro is preprocessor-style, it is just the sequence of characters, which happen to be within "". There is no type. The macro is expanded before the compiler (with its notion of types) starts the actual compilation.

2. C++ will always concatenate all character-sequences-within-"". "A" "B" will always be handled as "AB" during building. There is not operator, no implicit operator either. This is often used to have very long string literals, spanning several line in code.