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digitalmars.D.learn - extern (C) function call with const char * type will sometimes

reply "dysmondad" <raylwhitfield gmail.com> writes:
Since I've added this call, my program will sometimes but not 
always either generate a core dump or a seg fault. It seems that 
the issue is with the const char * parameter.

I don't have a good grasp of the difference between the way D and 
C work for char * types. The call to loadTexture uses a literal 
for the file name, i.e. "resources/ball.png".

// d lang bindings for C function
alias void SDL_Renderer;
alias void SDL_Texture;
extern (C) SDL_Texture * IMG_LoadTexture(SDL_Renderer * renderer, 
const char * file);

// d lang call to extern (C) function
SDL_Texture* loadTexture( SDL_Renderer * ren,  const char * file )
{
	SDL_Texture * loadedImage = IMG_LoadTexture( ren, file );
	return loadedImage;
}
Oct 15 2014
next sibling parent =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
On 10/15/2014 08:18 PM, dysmondad wrote:

 Since I've added this call, my program will sometimes but not always
 either generate a core dump or a seg fault. It seems that the issue is
 with the const char * parameter.

 I don't have a good grasp of the difference between the way D and C work
 for char * types. The call to loadTexture uses a literal for the file
 name, i.e. "resources/ball.png".

 // d lang bindings for C function
 alias void SDL_Renderer;
 alias void SDL_Texture;
 extern (C) SDL_Texture * IMG_LoadTexture(SDL_Renderer * renderer, const
 char * file);

 // d lang call to extern (C) function
 SDL_Texture* loadTexture( SDL_Renderer * ren,  const char * file )
 {
      SDL_Texture * loadedImage = IMG_LoadTexture( ren, file );
      return loadedImage;
 }
I wouldn't expect to see strings represented as 'const char *' on D side. The more convenient and safer option is to use 'string' on the D side and pass it through toStringz() before calling C. The D function now takes 'string' and calls toStringz() on it: SDL_Texture* loadTexture( SDL_Renderer * ren, string file ) { SDL_Texture * loadedImage = IMG_LoadTexture( ren, file.toStringz); return loadedImage; } However, note the lifetime issue: http://dlang.org/phobos/std_string.html#.toStringz Ali
Oct 15 2014
prev sibling parent reply Mike Parker <aldacron gmail.com> writes:
On 10/16/2014 12:18 PM, dysmondad wrote:
 Since I've added this call, my program will sometimes but not always
 either generate a core dump or a seg fault. It seems that the issue is
 with the const char * parameter.

 I don't have a good grasp of the difference between the way D and C work
 for char * types.
Strings in C are arrays of chars ending with the nul terminator. Strings in D are not required to be nul terminated. String literals in D *are* nul terminated. When passing a string to a C function that takes const char*, use toStringz as Ali showed in his post. --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com
Oct 16 2014
parent reply Mike Parker <aldacron gmail.com> writes:
On 10/16/2014 4:54 PM, Mike Parker wrote:
 On 10/16/2014 12:18 PM, dysmondad wrote:
 Since I've added this call, my program will sometimes but not always
 either generate a core dump or a seg fault. It seems that the issue is
 with the const char * parameter.

 I don't have a good grasp of the difference between the way D and C work
 for char * types.
Strings in C are arrays of chars ending with the nul terminator. Strings in D are not required to be nul terminated. String literals in D *are* nul terminated. When passing a string to a C function that takes const char*, use toStringz as Ali showed in his post.
Forgot to mention -- toStringz in std.string will add the nul terminator if it is not already there. --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com
Oct 16 2014
parent "dysmondad" <raylwhitfield gmail.com> writes:
On Thursday, 16 October 2014 at 07:55:24 UTC, Mike Parker wrote:
 On 10/16/2014 4:54 PM, Mike Parker wrote:
 On 10/16/2014 12:18 PM, dysmondad wrote:
 Since I've added this call, my program will sometimes but not 
 always
 either generate a core dump or a seg fault. It seems that the 
 issue is
 with the const char * parameter.

 I don't have a good grasp of the difference between the way D 
 and C work
 for char * types.
Strings in C are arrays of chars ending with the nul terminator. Strings in D are not required to be nul terminated. String literals in D *are* nul terminated. When passing a string to a C function that takes const char*, use toStringz as Ali showed in his post.
Forgot to mention -- toStringz in std.string will add the nul terminator if it is not already there. --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com
Thank you very much. Because of your help, my application has far fewer seg faults and core dumps. Now, if I can just figure out why the SDL_RenderPresent call is having problems. I suspect that has more to do with the way I'm using the library than the calling convention.
Oct 16 2014