Inconsistent results with fstream::read - c++

Question

My program use a small SQLite3 database. To make sure it actually exist when the program is launched, I have a database creation script in a file, that is executed.
The script work without problem.
However, when using C++ I/O functions to read from that file, I am getting really often invalid characters at the end of my file, which result in the script containing errors and not being properly executed by the SQLite library. Here is an example when displaying the buffer content:
// Proper content from the file, then a random character is there
1
Error executing request: near "1": syntax error
Other characters also appear, whitespaces, numbers, letters...
Here is the code where I load my script :
std::cerr << "Creating database if needed...\n";
char sql_script[] = "/path/to/script.sql";
int script_length;
bool result = false;
std::ifstream script_fs(sql_script, std::fstream::binary | std::fstream::in);
if (script_fs) {
char* buffer;
char** err_msg = NULL;
script_fs.seekg(0, script_fs.end);
script_length = script_fs.tellg();
script_fs.seekg(0, script_fs.beg);
buffer = new char[script_length];
script_fs.read(buffer, script_length);
std::cout << "sql:\n" << buffer << "\n";
if (sqlite3_exec(m_db, buffer, NULL, NULL, err_msg) == SQLITE_OK){
result = true;
} else {
std::cerr << "Error executing: " << sqlite3_errmsg(m_db) << "\n" << err_msg << "\n";
}
delete buffer;
script_fs.close();
} else {
std::cerr << "Error opening script: " << strerror(errno) << "\n";
}
return result;
}
Why is this happening and how can I fix this ?

Answer 1

You need to make sure that you have a null-terminated string.
Allocate memory for one more character.
Assign the null character to the last element of buffer.
buffer = new char[script_length+1];
script_fs.read(buffer, script_length);
buffer[script_length] = '\0';
Also, use the array form of delete.
delete [] buffer;

Answer 2

Don't mix C and C++, If you want to read sql query file in C++ using ifstream then below code in C++ can be one approach in which you don't need to manage memory, take care of things like allocating one extra char of '\0' etc. :
#include <iostream>
#include <fstream>
#include <vector>
using namespace std;
int main() {
ifstream fin("test.sql", std::fstream::binary | std::fstream::in);
std::string sqlquery = std::string(std::istreambuf_iterator<char>(fin), std::istreambuf_iterator<char>());
std::cout<<sqlquery<<std::endl;
return 0;
}