1 files changed, 26 insertions, 0 deletions
diff --git a/src/fs.c b/src/fs.c
new file mode 100644
index 0000000..a299ef9
--- /dev/null
+++ b/src/fs.c
@@ -0,0 +1,26 @@
+#include "fs.h"
+#include "std.h"
+
+// 'ext' must include '.'.
+char* replace_extension(const char* file_name, const char* ext) {
+    size_t len = strlen(file_name);
+    const char* last_slash = strrchr(file_name, '/');
+    const char* last_dot = strrchr(file_name, '.');
+
+    size_t ext_len = strlen(ext);
+    size_t base_len;
+    // !last_slash: foo.c
+    // last_slash < last_dot: ./bar/foo.c
+    if (last_dot && (!last_slash || last_slash < last_dot)) {
+        base_len = last_dot - file_name;
+    } else {
+        base_len = len;
+    }
+
+    char* result = calloc(base_len + ext_len + 1, sizeof(char));
+    memcpy(result, file_name, base_len);
+    memcpy(result + base_len, ext, ext_len);
+    result[base_len + ext_len] = '\0';
+
+    return result;
+}