c++ How to put path from command line argument to fprintf - c++

Question

I am having trouble figuring out how to take a path from the command line argument and having my program write to that folder using fprinf. For example: /here would write the file to the "here" folder with /here being the path from where the program is to where it needs to be written. Same for if the path were /there/here. This is just this section of my code:
void write_file(int sockfd, char* path)
{
int n;
FILE *fp;
char filename[] = "file1.txt";
char buffer[SIZE];
fp = fopen(filename, "w");
if (fp == NULL)
{
std::cerr << "ERROR: Could not write file.\n";
exit(EXIT_FAILURE);
}
while (1)
{
n = recv(sockfd, buffer, SIZE, 0);
if (n <= 0)
{
break;
return;
}
fprintf(fp, "%s", buffer);
bzero(buffer, SIZE);
}
fclose(fp);
return;
}
This code works but saves the file in my current folder. The variable "path" is the command line argument.
Edit: This is code that does not print lines to a file. Instead it copies lines from an existing file and puts those lines into the "file1.txt" file.

Answer 1

Here's an example using std::filesystem (C++17):
void write_file(int sockfd, const char* path)
{
auto filename = std::filesystem::path(path) / "file1.txt";
std::ofstream out{ filename, ios::trunc | ios::out };
if (!out) {
std::cerr << "ERROR: " << std::strerror(errno) << "\n";
exit(EXIT_FAILURE);
}
char buffer[SIZE];
while (1)
{
int n = recv(sockfd, buffer, sizeof(buffer), 0);
if (n == 0)
{
break;
}
if (n < 0) {
std::cerr << "ERROR: " << std::strerror(errno) << "\n";
break;
}
if (!out.write(buffer, n)) {
std::cerr << "ERROR: " << std::strerror(errno) << "\n";
break;
}
}
}
If you don't have std::filesystem support, you can replace the first 2 statements with some manual path concatenation like:
std::string filename = path;
if (filename != "" && filename.back() != '/')
filename += '/';
filename += "file1.txt";