Data commit

Task/Remove-lines-from-a-file/C/remove-lines-from-a-file.c

@@ -0,0 +1,61 @@
+#include <stdio.h>
+#include <stdlib.h> /* for atoi() and malloc() */
+#include <string.h> /* for memmove() */
+
+/* Conveniently print to standard error and exit nonzero. */
+#define ERROR(fmt, arg) return fprintf(stderr, fmt "\n", arg)
+
+int main(int argc, char **argv)
+{
+    FILE *fp;
+    char *buf;
+    size_t sz;
+    int start, count, lines = 1;
+    int dest = 0, src = 0, pos = -1;
+
+    /* Initialization and sanity checks */
+    if (argc != 4)
+        ERROR("Usage: %s <file> <start> <count>", argv[0]);
+
+    if ((count = atoi(argv[3])) < 1) /* We're a no-op. */
+        return 0;
+
+    if ((start = atoi(argv[2])) < 1)
+        ERROR("Error: <start> (%d) must be positive", start);
+
+    if ((fp = fopen(argv[1], "r")) == NULL)
+        ERROR("No such file: %s", argv[1]);
+
+    /* Determine filesize and allocate a buffer accordingly. */
+    fseek(fp, 0, SEEK_END);
+    sz = ftell(fp);
+    buf = malloc(sz + 1);
+    rewind(fp);
+
+    /* Fill the buffer, count lines, and remember a few important offsets. */
+    while ((buf[++pos] = fgetc(fp)) != EOF) {
+        if (buf[pos] == '\n') {
+            ++lines;
+            if (lines == start) dest = pos + 1;
+            if (lines == start + count) src = pos + 1;
+        }
+    }
+
+    /* We've been asked to do something weird; clean up and bail. */
+    if (start + count > lines) {
+        free(buf);
+        fclose(fp);
+        ERROR("Error: invalid parameters for file with %d lines", --lines);
+    }
+
+    /* Overwrite the lines to be deleted with the survivors. */
+    memmove(buf + dest, buf + src, pos - src);
+
+    /* Reopen the file and write back just enough of the buffer. */
+    freopen(argv[1], "w", fp);
+    fwrite(buf, pos - src + dest, 1, fp);
+
+    free(buf);
+    fclose(fp);
+    return 0;
+}