How to print String output to a file?-CodePudding

I´m trying to mod a little Program to write text from an Input window to textfile. I´m not very familiar with C and tested a little bit around.

void wr_wprintf(wr_window_t *window, wi_string_t *fmt, ...) {
        wi_string_t             *string;
        va_list                 ap;

        va_start(ap, fmt);
        string = wi_string_init_with_format_and_arguments(wi_string_alloc(), fmt, ap);
        va_end(ap);
        wr_wprint(window, string);

        FILE *fp;
        fp = fopen("/home/pi/test", "w");
        fprintf(fp, string);
        fclose(fp);

        wi_release(string);
}

The command wr_wprint(window, string); is the output of the text. As you can see I tried already something with fopen. But it did not write the text to file. The file is created but there is nothing inside.

CodePudding user response：

UPDATE

After getting access to the library repo being used, I found the definition of wi_string_t. It is part of the libwired submodule. From there, the definition of wi_string_t can be found in libwired/data/wi-string.c. The fact that it is defined inside a c file (traditionally) means your program does not know the contents of the struct. This means that wi_string_t* acts as an "opaque pointer". Since we must pretend not to know the contents of the struct, we must utilize the API functions defined in wi-string.h. I was able to find the following in there:

 93 WI_EXPORT wi_uinteger_t                     wi_string_length(wi_string_t *);
 94 WI_EXPORT const char *                      wi_string_cstring(wi_string_t *);
 95 WI_EXPORT char                              wi_string_character_at_index(wi_string_t *, wi_uinteger_t);

At line 94, we have the function wi_string_cstring. A function that returns a const char* to the data itself. This is exactly what we need.

The following should work for you, but I didn't compile the library to know for sure:

void wr_wprintf(wr_window_t *window, wi_string_t *fmt, ...) {
        wi_string_t             *string;
        va_list                 ap;

        va_start(ap, fmt);
       

        string = wi_string_init_with_format_and_arguments(wi_string_alloc(), fmt, ap);
        va_end(ap);
        wr_wprint(window, string);

        FILE *fp;
        fp = fopen("/home/pi/test", "w");
        if (fp == NULL) {
                // error handling
        } else {
                fputs(wi_string_cstring(string), fp);
                fclose(fp);
        }

        wi_release(string);
}