Several minor issues with the C language fopen function in Linux

In Linux, there are several minor issues with the C language fopen function-Linux general technology-Linux programming and kernel information. The following is a detailed description. 1. The difference between quotation marks when using fopen (File opening.

Char filename [20] = "NULL ";
Char directory [20] = "NULL ";

Printf ("please input the file name. \ n ");
Scanf ("% s", filename );

Fp = fopen ("filename", "w"); adding quotation marks will create a file in the current directory in the name of filename itself

Fp = fopen (filename, "w"); files are created in the current directory in the name of the array filename value without quotation marks.

If you want to create a file named after the array filename value in a directory, you can do the following:
Sprintf (directory, "/home/renewjoy/% s", filename); // sprintf can connect two strings

Or: strcpy (directory, "/home/renewjoy/"); // # include
Strcat (directory, filename );

Fp = fopen (directory, "w ");

2. In fopen, it seems that it cannot be parsed "~ "Symbol, but can parse". ","... "path.

Fp = fopen ("~ /Study/c/test. c "," w "); an error is returned.
Fp = fopen ("$ HOME/study/c/test. c", "w"); an error is returned.
Fp = fopen (/home/renewjoy/study/c/test. c, "w"); the absolute path must be used.
Fp = fopen ("../test. c", "w"); you can create the file test. c In the parent directory of the current directory.

3. open the file in write mode: fopen (". /open_file "," w "). The file content cannot be read. You must set the open mode to read and write:" w +"