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