ppm format that have magic code P3 - c

Question

how i can read ppm image that have magic code P3. in c language?
this code reading ppm image that have magic code P3 but there a problem with loading method,this code enters into in infinite loop when reading the value of pixles?
/* This is for reading and Writing images file in PPM
Also example of making Negative images
- Use this file as an example of reading (loading) and writing (storing) images files.
- This program loads an PPM image and store a new image that is the negative of the original image.
*/
typedef struct pdata {
int red;
int green;
int blue;
} pdata;
typedef struct ppm {
int w;
int h;
int max;
pdata *pData;
} ppm;
#include <stdio.h>
#include <math.h>
#include <stdlib.h>
//#define kernelW 3
//#define kernelH 3
//#define imageW 403
//#define imageH 332
char filename[256];
/*
This LoadPGM function is an updated version that will deal with
comments in file headers and do at least some basic checking if the
file can be opened or is the correct format. It does assume the file
is actually a valid length once the header has been read.
You are of course free to use your own file reading functions.
*/
void LoadPGM( char* filename, ppm* pPgm ) {
FILE* ifp;
int word;
int nRead = 0;
char readChars[256];
//open the file, check if successful
ifp = fopen( filename, "r" );
if (!ifp) {
printf("Error: Unable to open file %s.\n\n", filename);
exit(1);
}
//read headers from file
printf ("Reading PPM file: %s...\n", filename);
fscanf (ifp, "%s", readChars);
if (strcmp(readChars, "P3") == 0) {
//valid file type
//get a word from the file
fscanf (ifp, "%s", readChars);
while (readChars[0] == '#') {
//if a comment, get the rest of the line and a new word
fgets (readChars, 255, ifp);
fscanf (ifp, "%s", readChars);
}
//ok, comments are gone
//get width, height, color depth
sscanf (readChars, "%d", &pPgm->w);
fscanf (ifp, "%d", &pPgm->h);
fscanf (ifp, "%d", &pPgm->max);
// allocate some memory, note that on the HandyBoard you want to
// use constant memory and NOT use calloc/malloc
pPgm = (ppm *)malloc(sizeof(ppm));
pPgm->pData = (pdata*)malloc(pPgm->w *pPgm->h * sizeof(pPgm->pData));
fscanf(ifp, "%d" ,&word);
pPgm->pData[0].red = word;
printf (" %d \n", word);
for (nRead = 0; nRead < pPgm->w * pPgm->h; nRead++) {
fscanf(ifp, "%d" ,&word);
// printf (" %d \n",word);
pPgm->pData[nRead].red = word;
fscanf(ifp, "%d" ,&word);
pPgm->pData[nRead].green = word;
fscanf(ifp, "%d" ,&word);
pPgm->pData[nRead].blue = word;
}
printf ("Loaded PPM. Size: %dx%d, Greyscale: %d \n",
pPgm->w, pPgm->h, pPgm->max + 1);
}
else {
printf ("Error: Read file type %s. Format unsupported.\n\n", readChars);
exit(1);
}
fclose(ifp);
}
/* Simply saves the PGM file to a file whose name is in filename */
void WritePGM( char* filename, ppm* pPgm ) {
FILE* ofp;
int w, h, max;
int nWrite = 0;
int i,j;
strcat(filename, ".out.ppm");
ofp = fopen(filename, "w");
if (!ofp) {
printf("Error: Unable to open file %s.\n\n", filename);
exit(1);
}
printf ("Writing ouput PPM: %s\n\n", filename);
//write the header
fprintf( ofp, "P3\n" );
fprintf( ofp, "%d %d\n", pPgm->w, pPgm->h );
// printf("Done. Have a nice day...\n\n");
fprintf( ofp, "%d\n", pPgm->max );
//write the image data
for (i = 0; i < pPgm->h;i++) {
for (j = 0; j < pPgm->w; j++)
fprintf(ofp,"%d ",*(pPgm->pData + i * pPgm->w + j));
fprintf(ofp,"\n");
}
fclose(ofp);
}
int main(int argc, char * argv[]) {
ppm* image, *r1,*r2;
// char filename[256];
int val;
int errchk;
char f1[256];
//check if a filename was given, if not, ask for one
if (argc > 1) {
strcpy(filename, argv[1]);
}
else {
printf ("Enter filename: ");
scanf ("%s", filename);
}
//allocate memory for the pgm struct
image = (ppm *) malloc (sizeof(ppm));
//read the file
LoadPGM(filename, image);
int h,w;
w=image->w;
h=image->h;
int* pBuff1;
int* pBuff2;
int size;
int sum=0;
WritePGM(filename, image);
// end of the program
}

Answer 1

This line
malloc(pPgm->w *pPgm->h * sizeof(pPgm->pData))
allocates the wrong size. It allocates sizeof(pointer) while you need it sizeof(pdata), your own RGB struct.
Typically, one only needs RGB as 3 unsigned char, and had you used that the error would have been invisible, since pointers are usually 4 bytes long (and nowadays can even be longer). But since you made your values each an int, the structure uses 12 bytes in total. Somewhere after the first third has been read (give or take), your code starts overwriting other stuff in memory and you get toasted.