Extract OGGs from stuff

oggextract.cpp

#include <cstdio>
#include <cstdlib>
#include <numeric>
#include <unistd.h>

bool test_header(FILE* f, int magic = 2){
	bool r = false;
	char buf[5];
	fread(buf, 1, 5, f);
	
	if(buf[0] == 'g' && buf[1] == 'g' && buf[2] == 'S' && !buf[3] && (buf[4] & magic)){
		r = true;
	}
	
	fseek(f, -5, SEEK_CUR);
	
	return r;
}

void write_ogg(FILE* in, size_t sz, int* n){
	char fname[32];
	char* buf = new char[sz];
	fread(buf, 1, sz, in);
	
	do {
		sprintf(fname, "%s%d.ogg", "extract_", (*n)++);
	} while(access(fname, F_OK) != -1);
	
	FILE* out = fopen(fname, "wb");
	fwrite(buf, 1, sz, out);
	fclose(out);
	
	delete [] buf;
}

void do_extract(FILE* f, int* n){
	int c = 0;
	long start = ftell(f), end = start;
	
	while(c = fgetc(f), !feof(f)){	
		if(c == 'O' && test_header(f, 4)){
			fseek(f, 25, SEEK_CUR);
			int nsegs = fgetc(f), total = 0;
	
			unsigned char buf[nsegs];
			fread(buf, 1, nsegs, f);
			
			total = std::accumulate(buf, buf+nsegs, 0);
			end = ftell(f) + total + 1;
			
			fseek(f, start-1, SEEK_SET);
			
			write_ogg(f, end - start, n);
			break;
		}
	}

}

inline void quit(const char* name, const char* msg){
	fprintf(stderr, "%s: %s\n", name, msg);
	exit(1);
}

int main(int argc, char** argv){
	if(argc < 2) quit(argv[0], "No argument given.");
	
	int c = 0, n = 0;
	
	for(int i = 1; i < argc; ++i){
		FILE* f = fopen(argv[i], "rb");
		if(!f) quit(argv[0], "File not found.");
		
		while(c = fgetc(f), !feof(f)){	
			if(c == 'O' && test_header(f)){
				do_extract(f, &n);
			}
		}
	}
	
	return 0;
}