CODEWITHSUNDEEP
iphonexcodelibpng
Nitzan Wilnai
Nitzan Wilnai

Reputation: 943

Problems using libpng in iPhone project

I am trying to add libpng to my iPhone project.

I copied the .c and .h files to their own directory "thirdparty/libpng/" and I included png.h in my texture class:

#ifndef PNG_H
    #include "thirdparty/libpng/png.h"
#endif

At this point my project compiles great with no warnings and errors.

Next I tried adding a function to check if a texture is a png, and I get a compile error on png_sig_cmp, even though png.h is included:

#define PNG_BYTES_TO_CHECK 4
int GETexture::CheckIfValidPNGTexture( const char* pTextureName, FILE **ppFp )
{
    char buf[PNG_BYTES_TO_CHECK];

    /* Open the prospective PNG file. */
    if ((*ppFp = fopen(pTextureName, "rb")) == NULL)
        return 0;

    /* Read in some of the signature bytes */
    if (fread(buf, 1, PNG_BYTES_TO_CHECK, *ppFp) != PNG_BYTES_TO_CHECK)
        return 0;

    /* Compare the first PNG_BYTES_TO_CHECK bytes of the signature.
     Return nonzero (true) if they match */

    return(!png_sig_cmp(buf, (png_size_t)0, PNG_BYTES_TO_CHECK)); // <- COMPILE ERROR

}

The error I get is: No matching function for call to 'png_sig_cmp'

The header is definitely getting included. If I try to type something random in it like "sdfdd" I get a compile error, showing it is parsing that header file.

Any ideas?

Upvotes: 2

Views: 1483

Answers (1)

seeoneself
seeoneself

Reputation: 95

I had exactly the same problem once and what helped me was simple casting - because if you look into png.h header file , png_sig_cmp definition :

 png_sig_cmp(png_const_bytep sig, png_size_t start, png_size_t num_to_check)

First parameter is png_const_bytep - which is defined as : 

PNG_CONST png_byte        FAR * png_const_bytep

which translated really as : 

const unsigned char*

I would simple typecast :

return(!png_sig_cmp((png_const_bytep)buf, (png_size_t)0, PNG_BYTES_TO_CHECK));

Hope it helps!

Upvotes: 3

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