pad.c

Pad a file to desire file size under Linux

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>


int main(int argc, char *argv[])
{
	FILE *infp, *outfp;
	int target_size, input_size;
	int unit, i;
	char buffer[512];
	unsigned char fill_char;

	if(argc!=5)
	{
		printf("Argument number invalid\n");
		printf("pad <size> <input file> <output file> <fill char>\n");
		exit(1);
	}
	
	fill_char=strtoul(argv[4], 0, 0);

	i=strlen(argv[1]);
	unit=argv[1][i-1];
	switch(unit)
	{
		case 'g':
		case 'G':
			argv[1][i-1]=0;
			target_size=(int)(atof(argv[1])*1024*1024*1024);
			break;
		case 'M':
		case 'm':
			argv[1][i-1]=0;
			target_size=(int)(atof(argv[1])*1024*1024);
			break;
		case 'k':
		case 'K':
			argv[1][i-1]=0;
			target_size=(int)(atof(argv[1])*1024);
			break;
		case '0'...'9':
			target_size=(int)(atof(argv[1]));
			break;
		default:
			printf("Unknown size input\n");
			exit(1);
	}

	infp=fopen(argv[2], "rb");
	outfp=fopen(argv[3], "wb");

	if(!infp || !outfp)
	{
		printf("Open file error\n");
		exit(1);
	}
	input_size=0;
	while(!feof(infp))
	{
		i=fread(buffer, 1, 512, infp);
		if(i<0)
		{
			printf("Error in reading input file: err %d\n", i);
			exit(1);
		}
		if(i==0)
			continue;
		i=fwrite(buffer, 1, i, outfp);
		if(i<=0)
		{
			printf("Error in writing output file\n");
			exit(1);
		}
		input_size+=i;
	}

	i=target_size-input_size;
	printf("Target input size in byte : %10d(0x%08x)\n", input_size, input_size);	
	printf("Target output size in byte: %10d(0x%08x)\n", target_size, target_size);	
	printf("Filling %-5d(0x%08x) bytes with hex 0x%02x\n", i, i,fill_char);
	if(i>4)
	{
		int k;
		unsigned char *marker;

		for(k=0;k<(i-4);k++)
			fputc(fill_char, outfp);

		marker=(unsigned char *)&input_size;

		fputc(marker[0], outfp);
		fputc(marker[1], outfp);
		fputc(marker[2], outfp);
		fputc(marker[3], outfp);
	}
	else if(i>0)
	{
		printf("Not enough space to insert size marker at bottom\n");
		goto err;
	}
	else
	{
		printf("Target size smaller than the input file size\n");
		goto err;
	}
	fclose(infp);
	fclose(outfp);
	return 0;	
err:
	fclose(infp);
	fclose(outfp);
//	unlink(argv[3]);
	exit(1);

}