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/* An attempt to write a PNG file that can be read be the likes of
Mozilla/IE/the GIMP. It will only uses a very small portion of the
available functionality of PNG. All I want is to be able to create
images.
*/
#include <string>
#include <png.h>
using namespace std;
class PNGImage {
string filename;
FILE* fp;
public:
PNGImage() : fp(NULL) {}
PNGImage(string _filename) : filename(_filename), fp(NULL) {}
~PNGImage();
bool isPNG(int bytesToCheck);
private:
bool openFile();
};
PNGImage::~PNGImage() {
if (fp!=NULL) fclose(fp);
}
bool PNGImage::openFile() {
if (fp!=NULL) {
printf("file already opened\n");
return false; // can't open an already opened file
}
fp = fopen(filename.c_str(), "rb");
if (!fp) {
printf("couldn't open file %s\n", filename.c_str());
return false; // couldn't open file
}
printf("opened file %s\n", filename.c_str());
return true;
}
bool PNGImage::isPNG(int bytesToCheck = 8) {
if (fp==NULL) {
if (openFile() == false) return false;
}
if (bytesToCheck > 8) {
bytesToCheck=8;
printf("bytesToCheck set to 8. It cannot be more than 8.\n");
}
else if (bytesToCheck < 1) {
bytesToCheck=1;
printf("bytesToCheck set to 1. It cannot be less than 1.\n");
}
// todo: check that fp is at start of file.
char header[8]; // 8 is than maximum size that can be checked.
int retValue = fread(header, 1, bytesToCheck, fp);
if (retValue != bytesToCheck) {
printf("couldn't read %d bytes from file.\n", bytesToCheck);
}
// use library to check if it's a valid PNG file
bool valid;
valid = ( png_sig_cmp((png_byte*)header, 0, bytesToCheck) == 0);
return valid;
}
int main(int argc, char* argv[]) {
// open file depending on argument passed from command line
string filename("pngtest.png");
if (argc==2) filename.assign(argv[1]);
PNGImage image(filename);
if (image.isPNG()) printf("file is PNG image\n");
else printf("file is not PNG image\n");
printf("finished.\n");
return 0; // success
}
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