www.digitalmars.com         C & C++   DMDScript  

digitalmars.D.learn - "need `this` for `s` of type `char*`" error message

reply rempas <rempas tutanota.com> writes:
After not being able to use ImportC to automatically compile a C 
library, now I'm trying to do it myself. The library I want to 
use is [tomlc99](https://github.com/cktan/tomlc99) which is a 
small C library to parse toml files. Now I compiled the library 
and I copied the "config.h" file and modified to make it a D file 
that will contain the declaration so D knows which symbols to 
call. I resulted with a "toml.d" file and a "main.d" file. The 
first one contains the decorations and the second one contains 
the code from the example in the 
[usage](https://github.com/cktan/tomlc99#usage) section. However, 
when I try to compile, I'm getting the following error message:

```
main.d(51): Error: need `this` for `s` of type `char*`
Deprecation: argument `__error` for format specification `"%s"` 
must be `char*`, not `_error_`
main.d(57): Error: need `this` for `i` of type `long`
main.d(63): Error: need `this` for `s` of type `char*`
```

I uploaded the modified files so someone is able to look at them 
and explain me what I'm doing wrong so I can properly learn. 
Links:

[toml.d](https://gist.github.com/rempas/8aaab43b71e3da720ce298ef472f0673)
[main.d](https://gist.github.com/rempas/07dfb15295c5f6142c6a8dfab669c40e)
Nov 10 2021
parent reply Mathias LANG <geod24 gmail.com> writes:
On Thursday, 11 November 2021 at 07:04:57 UTC, rempas wrote:

 After not being able to use ImportC to automatically compile a 
 C library, now I'm trying to do it myself. The library I want 
 to use is [tomlc99](https://github.com/cktan/tomlc99) which is 
 a small C library to parse toml files. Now I compiled the 
 library and I copied the "config.h" file and modified to make 
 it a D file that will contain the declaration so D knows which 
 symbols to call. I resulted with a "toml.d" file and a "main.d" 
 file. The first one contains the decorations and the second one 
 contains the code from the example in the 
 [usage](https://github.com/cktan/tomlc99#usage) section. 
 However, when I try to compile, I'm getting the following error 
 message:

 ```
 main.d(51): Error: need `this` for `s` of type `char*`
 Deprecation: argument `__error` for format specification `"%s"` 
 must be `char*`, not `_error_`
 main.d(57): Error: need `this` for `i` of type `long`
 main.d(63): Error: need `this` for `s` of type `char*`
 ```

 I uploaded the modified files so someone is able to look at 
 them and explain me what I'm doing wrong so I can properly 
 learn. Links:

 [toml.d](https://gist.github.com/rempas/8aaab43b71e3da720ce298ef472f0673)
 [main.d](https://gist.github.com/rempas/07dfb15295c5f6142c6a8dfab669c40e)


     Your type definition is wrong:
     ```D
     struct toml_datum_t {
       int ok;
       union u {
         toml_timestamp_t* ts; /* ts must be freed after use */
         char*   s; /* string value. s must be freed after use */
         int     b; /* bool value */
         int64_t i; /* int value */
         double  d; /* double value */
       }
     }
     ```

     If you check the size of this struct, it's going to be 4, 
because `u` is a type definition. What you want is either:
     ```D
     struct toml_datum_t {
       int ok;
       union {
         toml_timestamp_t* ts; /* ts must be freed after use */
         char*   s; /* string value. s must be freed after use */
         int     b; /* bool value */
         int64_t i; /* int value */
         double  d; /* double value */
       }
     }
     ```

     Which you access via `host.s` or:
     ```D
     struct toml_datum_t {
       int ok;
       /// This is the type definition
       union U {
         toml_timestamp_t* ts; /* ts must be freed after use */
         char*   s; /* string value. s must be freed after use */
         int     b; /* bool value */
         int64_t i; /* int value */
         double  d; /* double value */
       }
       /// This is the field
       U u;
     }
     ```

Note that instead of doing this work yourself, I would highly 
recommend the excellent 
[dstep](https://github.com/jacob-carlborg/dstep).
Nov 10 2021
parent reply Mathias LANG <geod24 gmail.com> writes:
On Thursday, 11 November 2021 at 07:10:39 UTC, Mathias LANG wrote:

 [...]


Your type definition is wrong:
```D
struct toml_datum_t {
   int ok;
   union u {
     toml_timestamp_t* ts; /* ts must be freed after use */
     char*   s; /* string value. s must be freed after use */
     int     b; /* bool value */
     int64_t i; /* int value */
     double  d; /* double value */
   }
}
```

If you check the size of this struct, it's going to be 4,
because `u` is a type definition. What you want is either:

```D
struct toml_datum_t {
   int ok;
   union {
     toml_timestamp_t* ts; /* ts must be freed after use */
     char*   s; /* string value. s must be freed after use */
     int     b; /* bool value */
     int64_t i; /* int value */
     double  d; /* double value */
   }
}
```

Which you access via `host.s` or:

```D
struct toml_datum_t {
   int ok;
   /// This is the type definition
   union U {
     toml_timestamp_t* ts; /* ts must be freed after use */
     char*   s; /* string value. s must be freed after use */
     int     b; /* bool value */
     int64_t i; /* int value */
     double  d; /* double value */
   }
   /// This is the field
   U u;
}
```

Note that instead of doing this work yourself, I would highly 
recommend the excellent 
[dstep](https://github.com/jacob-carlborg/dstep).

Fixed formatting (so much for "Fix it for me").
Nov 10 2021
parent rempas <rempas tutanota.com> writes:
On Thursday, 11 November 2021 at 07:15:04 UTC, Mathias LANG wrote:

 [...]

 Note that instead of doing this work yourself, I would highly 
 recommend the excellent 
 [dstep](https://github.com/jacob-carlborg/dstep).

 Fixed formatting (so much for "Fix it for me").


Oh, now it makes sense! Thanks a lot! I will learn and use dstep 
in the future! Have an amazing day!
Nov 10 2021