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copied!<p>Here's a solution similar to @adam-rosenfields in-place modification routine but without needlessly resorting to strlen(). Like @jkramer, the string is left-adjusted within the buffer so you can free the same pointer. Not optimal for large strings since it does not use memmove. Includes the ++/-- operators that @jfm3 mentions. <a href="http://fctx.wildbearsoftware.com" rel="nofollow">FCTX</a>-based unit tests included.</p> <pre><code>#include <ctype.h> void trim(char * const a) { char *p = a, *q = a; while (isspace(*q)) ++q; while (*q) *p++ = *q++; *p = '\0'; while (p > a && isspace(*--p)) *p = '\0'; } /* See http://fctx.wildbearsoftware.com/ */ #include "fct.h" FCT_BGN() { FCT_QTEST_BGN(trim) { { char s[] = ""; trim(s); fct_chk_eq_str("", s); } // Trivial { char s[] = " "; trim(s); fct_chk_eq_str("", s); } // Trivial { char s[] = "\t"; trim(s); fct_chk_eq_str("", s); } // Trivial { char s[] = "a"; trim(s); fct_chk_eq_str("a", s); } // NOP { char s[] = "abc"; trim(s); fct_chk_eq_str("abc", s); } // NOP { char s[] = " a"; trim(s); fct_chk_eq_str("a", s); } // Leading { char s[] = " a c"; trim(s); fct_chk_eq_str("a c", s); } // Leading { char s[] = "a "; trim(s); fct_chk_eq_str("a", s); } // Trailing { char s[] = "a c "; trim(s); fct_chk_eq_str("a c", s); } // Trailing { char s[] = " a "; trim(s); fct_chk_eq_str("a", s); } // Both { char s[] = " a c "; trim(s); fct_chk_eq_str("a c", s); } // Both // Villemoes pointed out an edge case that corrupted memory. Thank you. // http://stackoverflow.com/questions/122616/#comment23332594_4505533 { char s[] = "a "; // Buffer with whitespace before s + 2 trim(s + 2); // Trim " " containing only whitespace fct_chk_eq_str("", s + 2); // Ensure correct result from the trim fct_chk_eq_str("a ", s); // Ensure preceding buffer not mutated } // doukremt suggested I investigate this test case but // did not indicate the specific behavior that was objectionable. // http://stackoverflow.com/posts/comments/33571430 { char s[] = " foobar"; // Shifted across whitespace trim(s); // Trim fct_chk_eq_str("foobar", s); // Leading string is correct // Here is what the algorithm produces: char r[16] = { 'f', 'o', 'o', 'b', 'a', 'r', '\0', ' ', ' ', 'f', 'o', 'o', 'b', 'a', 'r', '\0'}; fct_chk_eq_int(0, memcmp(s, r, sizeof(s))); } } FCT_QTEST_END(); } FCT_END(); </code></pre>

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