gdImageCreateFromPng / fopen

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <gd.h>
 
#define BUF_SIZE	1024
#define MAX_URL_LEN	1024
 
char url[MAX_URL_LEN];		// URL String
char fileName[BUF_SIZE];	// File Name
 
int dw_file();
int make_rgb_file();
 
int main(int argc, char *argv[])
{
	if(argv[1]!=0) {
		strncpy(url, argv[1], MAX_URL_LEN);
	} else {
		printf("ERROR: URL input error!\n");
		return -1;
	}
 
	/* download file from URL */
	dw_file();	
	/* extract the extension and call the function */
	make_rgb_file();
	return 0;
}
 
int dw_file()
{
	char wg_cmd[BUF_SIZE] = "wget ";		// wget command
	char wg_cmd_opt[100] = " -P /tmp -nH -r";
	char bn_cmd[BUF_SIZE] = "basename ";		// basename command
	FILE *bn_result;
 
	/* command: wget [URL] -P /tmp -nH -r
	   -P /tmp: set download directory
	   -nH: no host-directories
	   -r: re-downloading and overwriting */
	strncat(wg_cmd, url, BUF_SIZE);
	strncat(wg_cmd, wg_cmd_opt, BUF_SIZE);
	/* command: basename [URL] */
	strncat(bn_cmd, url, BUF_SIZE);
 
	/* execute wget shell command */
	if(system(wg_cmd)!=0) {
		printf("ERROR: wget command error!\n");
		return -1;
	}
	printf("\n\n");
 
	/* execute basename shell command and get file name */
	if((bn_result = popen(bn_cmd, "r"))!=0) {
		fgets(fileName, BUF_SIZE, bn_result);
		printf("FILENAME: %s\n", fileName);
	} else {
		printf("ERROR: basename command error!\n");
		return -1;
	}
	return 0;
}
 
int make_rgb_file()
{
	char *ext;
	char path[BUF_SIZE] = "/tmp/";
	FILE *fp;
	gdImagePtr im;
 
	ext = rindex(fileName, (int)'.');
	strncat(path, fileName, BUF_SIZE);
	printf("%s\n", path);
 
	if((fp=fopen(path, "rb")) == NULL ) {
		printf("ERROR: file open error!\n");
		return -1;
	} else {
		if(!strncmp(ext,".jpg",4) || !strncmp(ext,".jpeg",4) || 
		   !strncmp(ext,".JPG",4) || !strncmp(ext,".JPEG",4)) {
			printf("jpg area\n");
		} else if(!strncmp(ext,".gif",3) || !strncmp(ext,".GIF",3)) {
			printf("gif area\n");
		} else if(!strncmp(ext,".png",3) || !strncmp(ext,".PNG",3)) {
			printf("png area\n");
			if((im = gdImageCreateFromPng(fp))==NULL) {
				printf("ERROR: image create error!\n");
				return -1;
			} else {
				printf("%d %d\n", im->sx, im->sy);
			}
		} else printf("What is this?\n");
	}
	fclose(fp);
	gdImageDestroy(im);
	return 0;
}