c언어 strtoul 함수질문 드립니다,.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
#define Fclose(a) if (a != NULL) \
{\
    fclose(a); \
    a = NULL; \
}
#define COMMAND 16
 
 
int main(int argc, char *argv[]){
	if (argc != 5)
	{
		printf("error! program don't have four arguments");
		return 1;
	}
	FILE *tr;
	long adr;
	char pch[20],*buf,*temp;
	if ((tr = fopen(argv[1], "r")) == NULL)
	{
		perror("memory trace file");
		return -1;
	}
	else{
		/*parsing*/
		while (!feof(tr)){
			fgets(pch,COMMAND, tr);
			buf = strtok(pch, " ");
			buf = strtok(NULL, " ");
			//adr = atoi(buf);
			adr = strtoul(buf,NULL,10);
			printf("%s\n", buf);
		}
	}
	int n;
	printf("argc = %d\n", argc - 1);
	for (n = 1; n < argc; n++)
		printf("argv{%d} = %s\n", n, argv[n]);
	Fclose(tr);
	return 0;
}

while (!feof(tr)){
			fgets(pch,COMMAND, tr);
			buf = strtok(pch, " ");
			buf = strtok(NULL, " ");
			//adr = atoi(buf);
			adr = strtoul(buf,buf,10);
			printf("%s\n", buf);
		}

s 0x1fffff70 1
l 0x1fffff78 1
l 0x1fffff98 6
l 0x1fffffa0 2
l 0x1fffffa8 2
l 0x1fffffb0 2
l 0x1fffffb8 2
l 0x1fffffc0 2
l 0x1fffffc8 2
l 0x1fffffd0 2
l 0x1fffffd8 2
l 0x1fffffe0 2
l 0x1fffffe8 2
l 0x1ffffff0 2
l 0x1ffffff8 2
l 0x20000000 2
l 0x20000008 2
l 0x20000010 2

0x1fffffa8
0x1fffffa8
...
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<null>
...