Reading and writting PPM files

Question

0.00/5 (No votes)

See more:

I made following code to fast read and write ppm using smart code.
Unfortunately I have to use leelin() function to look if a text beginning with # is going to be read before reading xmax and ymax.
It is possible to look for "#" (following with text) at the file pointer before reading?

Here is the header of the PPM file:

P6
# CREATOR: GIMP PNM Filter Version 1.1
1280 720
255
(binary data)

What I have tried:

#include <iostream>
#pragma warning(disable:4996) //disable deprecateds
using namespace std;
typedef unsigned char uchar;

//Lee de ficheros:
void leelin(FILE *strin, char *linea);

bool read_image_ppm(char *filename, uchar  *&data, int &xmax1,int &ymax1);
bool save_image_ppm(char *filename, uchar  *data,int xmax,int ymax);

void main()
{
	uchar *data=NULL;
	int xmax,ymax;
	read_image_ppm("2944_1.ppm",data,xmax,ymax);
	save_image_ppm("out.ppm",data,xmax,ymax);
	delete data;
	cout<<"===END==="<<endl;getchar();
}


bool read_image_ppm(char *filename, uchar  *&data, int &xmax1,int &ymax1)
{
	xmax1=ymax1=0;
	FILE *str = fopen(filename, "rb");
	if (str == NULL) 	{ 		printf("Couldn't open %s for reading!\n", filename);getchar(); 		return false; 	}
	char linea[1024];
	leelin(str,linea);if(linea[0]!='P'||linea[1]!='6')  { 		printf("%s PPM file not type P6, so couldn't read! \n", filename);getchar();		return false; 	}
	leelin(str,linea);if(linea[0]=='#') leelin(str,linea);
	char *ptr=linea;xmax1=strtol(ptr,&ptr,10);ymax1=strtol(ptr+1,&ptr,10);leelin(str,linea);
	if (xmax1<1||xmax1>90000||ymax1<1||ymax1>90000) { 		printf("%s PPM file xmax or ymax is wrong= %i %i, so couldn't read! \n", filename,xmax1,ymax1);getchar();		return false; 	}
	data=new uchar[xmax1*ymax1*3];
	for (int j = 0; j < ymax1; j++) 
		fread(&data[3*j*xmax1], 1, 3*xmax1, str);
	fclose(str);
	return true;
}



bool save_image_ppm(char *filename, uchar  *data,int xmax1,int ymax1)
{
	FILE *output = fopen(filename, "wb");
	if (output == NULL)
	{
		printf("Couldn't open %s for writing!\n", filename);
		return false;
	}
	fprintf(output, "P6\n%d %d\n%d\n", xmax1, ymax1, 255);
	for (int j = 0; j < ymax1; j++) 
		fwrite(&data[3*j*xmax1], 1, 3*xmax1, output);
	fclose(output);
	return true;
}


void leelin(FILE *strin,char *linea)
{
	//removes 0x0D and 0x0A
	int i;
	linea[0]='\0';
	char *ptr=linea;
	for (i=0;(i<1024 && !feof(strin)); i++)
	{
		*ptr++ = fgetc(strin);
		//fscanf(strin, "%c", ptr++);  //OLD!!
		if (ptr[-1] == 10)
			break;
	}
	if (i>=1)
		ptr[-1]='\0';
	else
		linea[0]='\0';
	if (i>2 && ptr[-2]==0x0D)
		ptr[-2]='\0';
}

Posted 5-Sep-17 22:43pm

Javier Luis Lopez

Updated 5-Sep-17 23:08pm

Add a Solution

1 solution

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Jochen Arndt · Accepted Answer · 2017-09-05T23:08:00

Your leelin() function is already reading a line from the file into a buffer. So there should be no need for an additional check for comments before reading. Just ignore the line (which you are doing already in your code by reading the next line).

To skip comment lines, you might use something like

C++

do
    leelin(str,linea);
while (linea[0] == '#');

However, you may also read ahead by saving the file pointer before reading and restoring it after reading (see ftell - C++ Reference[^], fseek - C++ Reference[^] or fgetpos, fsetpos).

To read only a single character ahead you might also use ungetc - C++ Reference[^]:

C++

int readAhead = fgetc(str);
// Next read from stream will contain readAhead as first character
ungetc(readAhead, str);
if (readAhead == '#')
{
    // do something
}