How to copy text to array of characters in C

Question

I would like to copy text from text file to

How to copy text file to string in C?

 FILE *file; 
file = fopen ( filename, "r" );

and I assign it in variable like that

    // char P[] = "Content from File";

Answer 1

There's a couple ways this can be done. My personal favourite is to use fread() like this:

// Open the file the usual way.
File *file = fopen(filename, "r");
if(!file) exit(1); // Failed to open the file.

// Figure out the length of the file (= number of chars)
fseek(file, 0, SEEK_END);
long int size = ftell(file);
fseek(file, 0, SEEK_SET);

// Create the char-array and read the file-content.
char *P = malloc(size * sizeof(char)) // Allocate enough space.
if(!P) exit(2); // Failed to allocate memory.
fread(P, sizeof(char), size, file); // Read the file content.

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Here's an explanation as to how it works:

• fseek(file, 0, SEEK_END) Takes the file-stream file, and sets the stream-position to the end of the file (indicated by SEEK_END) with no offset (hence the 0). You can read more about this std-library function here.
• ftell(file) takes the file-stream file and returns the current stream-position (which we have previously set to be the end of the file, so this will give us the length of the entire file). This value is being returned as a long int. You can read more about it here.
• Now we have to set the stream-position back to the beginning, so that we can later read the file. This is being done with fseek() again, this time giving it the position-argument SEEK_SET. This tells it to jump back to the start of the file.
• We can now allocate our text-buffer, in your case called P. (After a malloc, don't forget to check if you actually got a valid pointer back!)
• Finally, we can read the file! fread() takes four arguments. The first one is the buffer to which we are going to write. This is the P char-array in your case. The second argument, sizeof(char), tells fread() what size the individual elements are going to be. In our case, we want to read characters, so we pass it the size of a character. The third argument is the length of the file, which we have previously determined. The last argument is the file-stream which should be read. If you want to read up on fread(), you can do that here.