ifstream read reading random char for the whole stream - c++

Question

I'm trying to implement the function from listing 5.1 here
but when copying into a buffer with read from a file I just get the same character (Í) for the whole array, where string.txt is a copy and paste from the previous link content.
Here is my code:
#include <iostream>
#include <fstream>
#include <string>
#include <cinttypes>
#include <cstdio>
#include <cstring>
const int block_size = 0x4000; //16KB
int search(char* buffer, int searchLength, char* stringToSearch, int stringToSearchLength) {
char * potentialMatch;
while (searchLength) {
potentialMatch = reinterpret_cast<char *>(memchr(buffer, *stringToSearch, searchLength));
if (potentialMatch == NULL)
break;
if (stringToSearchLength == 1) {
return 1;
} else {
if (!memcmp(potentialMatch + 1, stringToSearch + 1, stringToSearchLength - 1))
return 1;
}
searchLength -= potentialMatch - buffer + 1;
buffer = potentialMatch + 1;
}
return 0;
}
int main(int argc, char* argv[]) {
char *toSearch = "Interpreting Where";
int done = 0;
int found = 0;
char *buffer;
int64_t fileSizeLeft = 0;
std::ifstream myFile("string.txt");
if (!myFile.fail()) {
buffer = new char[block_size];
myFile.seekg(0, std::ios::end); //Get file's size
fileSizeLeft = myFile.tellg();
} else {
std::cout << "Cannot open file" << std::endl;
return 1;
}
int toSearchLength = strlen(toSearch);
int stringLeft = toSearchLength - 1;
int first_time = 1;
while (!done && fileSizeLeft > toSearchLength) {
if (first_time) {
myFile.read(buffer, block_size);
found = search(buffer, block_size, toSearch, toSearchLength);
} else {
memcpy(buffer, buffer + stringLeft, stringLeft);
myFile.read(buffer+stringLeft, fileSizeLeft-stringLeft);
found = search(buffer, block_size, toSearch, toSearchLength);
}
fileSizeLeft = fileSizeLeft - block_size;
first_time = 0;
}
if (found) {
std::cout << "String found" << std::endl;
} else {
std::cout << "String not found" << std::endl;
}
myFile.close();
delete[] buffer;
return 0;
}
I hope you can help me see what I'm doing wrong, thanks!

Answer 1

You are setting myFile's position to ios_base::end with seekg:
myFile.seekg(0, ios::end);
Then trying to read from it:
myFile.read(buffer, block_size);
Clearly no data will be read since myFile is already at ios_base::end. And you'll be reading whatever uninitialized data that was already in buffer
What you probably intended to do was to set your myFile position back to the beginning by doing this before reading:
myFile.seekg(0, ios::beg);