Newbie C/C++ struct array pointing to other struct array elements - c++

Question

I stumbled upon a neat trick that I've started using to write binary files into (flash) memory on arduino/esp8266 using a library someone posted to one of the esp8266 forums. I've been trying a number of ways to expand upon it. Most recently I've been minifying and compressing my web content files and compiling them in with sketches on my ESP.
The script he posted first uses the output of the unix command xxd -i to write the binary file into an array of hex. The second part uses a struct to combine the file details with a pointer to the array that you can reference from the code whenever the server gets a uri request that matches an entry in the array.
What I would like to do is create a second array of these things with 'default' tools already pre-compressed so I don't have to go through it every time and/or modify my script that builds the header file any time I create a new server sketch. Basically compress and xxd stuff like jquery.js, bootstrap.css and bootstrap.js (or more often their smaller counterparts like backbone or barekit)
Currently once a file is dumped to hex, for example:
FLASH_ARRAY(uint8_t, __js__simple_js,
0x1f, 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x03, 0x4b, 0x2b,
0xcd, 0x4b, 0x2e, 0xc9, 0xcc, 0xcf, 0x53, 0xc8, 0xad, 0xf4, 0xcf, 0xf3,
0xc9, 0x4f, 0x4c, 0xd1, 0xd0, 0xac, 0x4e, 0xcc, 0x49, 0x2d, 0x2a, 0xd1,
0x50, 0x0a, 0xc9, 0xc8, 0x2c, 0x56, 0x00, 0xa2, 0xc4, 0x3c, 0x85, 0xfc,
0xbc, 0x1c, 0xa0, 0x94, 0x42, 0x6e, 0x6a, 0x71, 0x71, 0x62, 0x7a, 0xaa,
0x92, 0xa6, 0x75, 0x51, 0x6a, 0x49, 0x69, 0x51, 0x9e, 0x42, 0x49, 0x51,
0x69, 0x6a, 0x2d, 0x00, 0x16, 0xa6, 0x25, 0xe5, 0x43, 0x00, 0x00, 0x00);
The existing code added them all at once along with the struct definition:
struct t_websitefiles {
const char* path;
const char* mime;
const unsigned int len;
const char* enc;
const _FLASH_ARRAY<uint8_t>* content;
} files[] = {
{
.path = "/js/simple.js",
.mime = "application/javascript",
.len = 84,
.enc = "gzip",
.content = &__js__simple_js,
},
{
/* details for file2 ...*/
},
{
/* details for file3 ...*/
}
};
Building an array of the structs representing the various files.
My questions amount to noob questions regarding the language syntax. Can I assume that I can use an identical populated struct in the place of what is inside the curly brackets? For example, if I had a second header file with my regularly used libraries, and jquery was compressed in an array called 'default_files' at position 3, could I use something like &default_files[3] in the place of { /* definitions stuffs */ }. Such as:
struct t_websitefiles {
const char* path;
const char* mime;
const unsigned int len;
const char* enc;
const _FLASH_ARRAY<uint8_t>* content;
} files[] = {
{
.path = "/js/simple.js",
.mime = "application/javascript",
.len = 84,
.enc = "gzip",
.content = &__js__simple_js,
},
&default_files[1],
&default_files[3],
{
.path = "/text/readme.txt",
.mime = "text/text",
.len = 112,
.enc = "",
.content = &__text__readme_txt,
}
};
(I'm guessing based on what I've learned thus far it needs the & in front of it?)
I also assume rather than re-writing the struct definition twice,I could do it as a typedef and then just do:
t_websitefiles files[] = { {/*definitions*/},{ /*stuffs*/ } };
Is that correct? Any help is appreciated. It's hard sometimes to find details on the syntax for specific use cases in documentation covering basics. (I would just try it, but I'm not conveniently in front of a compiler at the moment nor do I have direct access to my codebase but want to work on it later when I might not have direct access to the net)

Answer 1

From what I understand, you want create an array of structs such contains both compound literals and items from another array, all defined in header information.
I don't think this is possible - or at least not in the exact way you suggest. I'll try and provide an alternative though.
Can I assume that I can use an identical populated struct in the place of what is inside the curly brackets?
No - you're mixing your types. 'files' is defined as an array of 'struct t_website'.
The code
struct t_websitefiles files[] = {
...
&default_files[1],
...
}
won't compile as you are mixing your types. files is defined as an array of struct t_websitefile, but &default_files[1] is a pointer. C makes a distinction between pointers and non-pointers. They are seperate types.
The obvious option that I can see to do what you want is to use pointers. This will allow you to define everything in header information.
struct t_websitefiles default_files[] = {
....
}
struct t_websitefiles files[] = {
....
}
// An array of pointers
struct t_websitefiles *files_combined[] = {
&files[0],
&files[1],
&default_files[0],
// Or whatever values you want here
...
}
// Example main, just iterates through the combined list
// of files
int main(int argc, char* argv[]) {
int i;
int files_combined_len = sizeof(files_combined)/sizeof(struct t_websitefiles);
for (i=0; i<files_combined_len; i++) {
printf("File %s\r\n", files_combined[i]->path);
}
return 0;
}
Hope this helps.