вылезает segmentation fault. не понимаю где

const int bufferSize = 4096;
char buffer[bufferSize];
int currentFile = optind;
FILE *fp;

while (currentFile <= argc) {
if (currentFile != argc) {
    fp = fopen(argv[currentFile], "rb");
    if (fp == NULL) {
        fprintf(stderr, "%s: %s: net file",
        argv[0], argv[currentFile]);
        exit(1);
    }
}