Writing a file to users HOME directory in C

Question

I am trying to write a .txt file to the user's HOME directory.

I have tried:

char str[] = "TEST";
char* file = strcat(getenv("HOME"), "/dataNumbers.txt"); //I am concatenating the user's home directory and the filename to be created.
myFile = fopen(file,"w");
fwrite(str , 1 , sizeof(str) , myFile );

However, this does not create the file.

Answer 1

You are using strcat incorrectly.

 char *file;
 char *fileName = "/dataNumbers.txt";

 file = malloc(strlen(getenv("HOME") + strlen(fileName) + 1); // to account for NULL terminator
 strcpy(file, getenv("HOME"));
 strcat(file, fileName);

file will now contain the concatenated path and filename.

Obviously, this could be written much more cleanly. I'm just trying to be very straightforward.

Answer 2

You can't strcat() to an environment variable. You need another buffer:

char file[256]; // or whatever, I think there is a #define for this, something like PATH_MAX
strcat(strcpy(file, getenv("HOME")), "/dataNumbers.txt");
myFile = fopen(file,"w");

EDIT To address one of the comments below, you should first ensure that the data to be concatenated doesn't overflow the file buffer, or allocate it dynamically - not forgetting to free it afterwards.