Fix file operations

- Files not closed in read_file() and write_file()
 - New error messaging
 - Path stripping performed backwards

src/file.c

@@ -1,3 +1,4 @@
+#include <errno.h>
 #include <stdio.h>
 #include <string.h>
 
@@ -5,9 +6,12 @@
 
 
 const char* basename(const char* filename) {
-    const char* slash = filename;
-    for ( ; *slash && *slash != '\\' && *slash != '/'; ++slash);
-    return (*slash ? (&slash[1]) : filename);
+    const char* slash = filename + strlen(filename) - 1;
+    for ( ; slash >= filename &&
+            *slash != '\\' &&
+            *slash != '/';
+            --slash );
+    return &slash[1];
 }
 
 int replace_extension(char* filename, int max_len,
@@ -49,8 +53,15 @@ int write_file(const char* filename, const void* data, int len) {
     int status = -1;
 
     FILE* file = fopen(filename, "wb");
-    if (NULL != file && 1 == fwrite(data, len, 1, file)) {
-        status = 0;
+    if (NULL != file) {
+        if (1 == fwrite(data, len, 1, file)) {
+            status = 0;
+        } else {
+            fprintf(stderr, "Failed to write %d bytes from %s: %d\n", len, filename, errno);
+        }
+        fclose(file);
+    } else {
+        fprintf(stderr, "Failed to open %s: %d\n", filename, errno);
     }
 
     return status;
@@ -61,8 +72,15 @@ int read_file(const char* filename, void* data, int len) {
     int status = -1;
 
     FILE* file = fopen(filename, "rb");
-    if (NULL != file && 1 == fread(data, len, 1, file)) {
-        status = 0;
+    if (NULL != file) {
+        if (1 == fread(data, len, 1, file)) {
+            status = 0;
+        } else {
+            fprintf(stderr, "Failed to read %d bytes from %s: %d\n", len, filename, errno);
+        }
+        fclose(file);
+    } else {
+        fprintf(stderr, "Failed to open %s: %d\n", filename, errno);
     }
 
     return status;