Read a text file

03_inputs_and_outputs/.gitignore

 add_integers
+read_file

03_inputs_and_outputs/Makefile

@@ -5,11 +5,14 @@ CXX = g++
 CFLAGS = -Wall -O3
 
 .PHONY: all
-all: add_integers
+all: add_integers read_file
 
 add_integers: add_integers.c
-	$(CC) $(CFLAGS) -o add_integers add_integers.c
+	$(CC) $(CFLAGS) -o $@ $<
+
+read_file: read_file.c
+	$(CC) $(CFLAGS) -o $@ $<
 
 .PHONY: clean
 clean:
-	rm add_integers
+	rm add_integers read_file

03_inputs_and_outputs/read_file.c

+#include <stdio.h>
+
+int main() {
+    int c;
+    FILE *file;
+
+    // The second argument indicates that we just want to read the file. (We'd put "w" if we wanted
+    // to write instead.)
+    file = fopen("test.txt", "r");
+
+    // The file might not have opened successfully. For instance if "test.txt" doesn't exist.
+    if (file) {
+        // We read characters from the file one at a time, and print them. There are more efficient
+        // ways to load the data if you want to deal with bigger files, but this gets you pretty
+        // far, especially compared to scripting languages.
+        while ((c = getc(file)) != EOF) {
+            // This is like printf, but for only one character.
+            putchar(c);
+        }
+        fclose(file);
+    }
+}

03_inputs_and_outputs/test.txt

+This text is in a file.