lines: add null check after opening infile

.gitignore

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+# this is a comment
+
+# can we ignore any file without an extension?
+
+copy
+out.txt

c_programming/files/files.txt

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+Reading and Writing Files in C
+
+copy - copy one file to a new file, one letter at a time.
+
+lines - read lines from a text file using fgets.
+todo: lines_2 - remove the \n from the end of each line.
+https://stackoverflow.com/questions/2693776/removing-trailing-newline-character-from-fgets-input 
+https://man.freebsd.org/cgi/man.cgi?query=strcspn&sektion=3 

c_programming/files/lines.c

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+// A program that iterates one line at a time.
+// uses fgets.
+// https://manual.cs50.io/3/fgets
+
+// read the lines from lines.txt and print them out.
+
+#include <stdio.h>
+
+// char *fgets(char s[restrict .size], int size, FILE *restrict stream);
+
+// reads in at most one less than size characters from stream and stores them
+// into the buffer pointed to by s. Reading stops after an EOF or a newline.
+// If a newline is read, it is stored into the buffer. A terminating null byte
+// ('\0') is stored after the last character in the buffer.
+
+// lines.c is based on the example at https://en.cppreference.com/c/io/fgets
+
+
+#define SIZE 64
+
+int main(void)
+{
+    FILE* infile = fopen("lines.txt", "r");
+    if (infile == NULL)
+    {
+        perror("Failed to open in.txt");
+        return 1;
+    }
+    char buf[SIZE];
+
+    while (fgets(buf, sizeof buf, infile) != NULL)
+    {
+        printf("%s", buf);
+    }
+
+    if (feof(infile))
+    {
+        puts("End of file reached");
+    }
+
+    return 0;
+}

c_programming/files/lines.txt

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+Line one
+Line two
+
+Line four

git/ignore_compiled.txt

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+To make git ignore compiled C programs, we put this in the git ignore.

git/start_ignoring_me.txt

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+To make git ignore things, we need a gitignore.
+Here is how to get started with that.
+
+A tool for creating gitignore things: https://www.toptal.com/developers/gitignore/
+
+Of course, there is official documentation for git ignore: https://git-scm.com/docs/gitignore
+