Member Avatar for shanki himanshu

i am using strrev function and also included the header file string.h but i am getting the compile error
‘strrev’ was not declared in this scope.

what else is required?

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This error happens because strrev is not part of the C or C++ standard libraries. Some Windows toolchains expose Microsoft’s nonstandard _strrev, so it can appear to work locally (e.g., certain Dev-C++ setups) but fail on stricter compilers and online judges. The standard <string.h> does not include strrev, which is why you see the compile error. See the C header list for confirmation, and Microsoft’s docs for the vendor-specific _strrev. C <string.h> functions. MSVC _strrev.

As and said, write your own. Here’s a small, portable C version that works in place:

#include <string.h>

char *strrev_inplace(char *s) {
    if (!s) return NULL;
    size_t i = 0, j = strlen(s);
    if (j == 0) return s;
    for (--j; i < j; ++i, --j) {
        char t = s[i];
        s[i] = s[j];
        s[j] = t;
    }
    return s;
}

Notes:

  • Pass a modifiable array, not a string literal. For example:
    • OK: char buf[] = "hello"; strrev_inplace(buf);
    • Not OK: strrev_inplace("hello"); // modifies read-only storage
  • If you need a reversed copy, allocate a new buffer and copy characters from the end to the start.

If you’re actually compiling as C++ (your error text suggests g++), prefer the standard algorithm instead of strrev:

#include <algorithm>
#include <string>
std::string s = "hello";
std::reverse(s.begin(), s.end());  // portable

Reference for std::reverse: std::reverse.

This aligns with ’s and ’s points: portability beats extensions, especially on judge systems.

Recommended Answers

All 6 Replies

Member Avatar for rithish

can i know wat compiler r u using???

Member Avatar for rithish

some times the compilerdirectory may not have string.h libraray functions.the same problem i had in alloc.h

Member Avatar for deceptikon

strrev() isn't a standard function, so compilers aren't obligated to support it. What compiler are you using?

Member Avatar for np complete

You can always write your own strrev().

Member Avatar for shanki himanshu

in dev-c++ it works fine.
but the problem is when i submit the code on site. it gives me compile error.

Member Avatar for WaltP

Then, as deceptikon says, it's not supported by that compiler. Write your own.

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