bsearch()関数で文字列を探すサンプルコードです。

bsearch.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>


// Macros for restrict-qualifier under various environmets
#if _MSC_VER >= 1400                // In Visual C++ (after Visual C++ 2005),
#  define restrict      __restrict  // 'restrict' and '__inline__' aren't available
#  define __restrict__  __restrict  // but '__restrict' is.
#elif __cplusplus                   // In language C++ (but not Visual C++),
#  define restrict      __restrict  // 'restrict' isn't available but '__restrict' is.
#elif !defined(__STDC_VERSION__) || __STDC_VERSION__ < 199901L
#  if defined(__GNUC__)             // In gcc,
#    define restrict    __restrict  // 'restrict' isn't available but '__restrict' is.
#  else
#    define restrict                // If 'restrict' isn't available, remove 'restrict'
#    define __restrict              // as well as '__restrict'
#    define __restrict__            // and '__restrict__'.
#  endif
#endif

// LAMBDA for C/C++
#if defined(__cplusplus)
#  define LAMBDA(rettype, ARG_LIST, BODY)  \
     ([&]ARG_LIST -> rettype { BODY; } )
#elif defined(__GNUC__) && !defined(__clang__)
#  define LAMBDA(rettype, ARG_LIST, BODY)   \
   ({                                       \
     rettype __lambda_funcion__ ARG_LIST {  \
       BODY;                                \
     }                                      \
     __lambda_funcion__;                    \
   })
#else
#  error You have to compile with gcc or C++0x Compiler!!
#endif

#define LENGTH(array)  (sizeof(array) / sizeof((array)[0]))

#ifndef __cplusplus
#  define ARRAY_SIZE  40
#else
static const int ARRAY_SIZE = 40;
#endif


int main(void) {
  const char *table[] = {
    "Japan",
    "America",
    "Italy",
    "Thailand",
    "Mexico",
    "Russia"
  };
  char   str[ARRAY_SIZE];
  char   target[ARRAY_SIZE];
  char **search_result;

  qsort(table, LENGTH(table), sizeof(char *),
    LAMBDA(int, (const void *restrict a, const void *restrict b), {
      return strcmp(*(char **)a, *(char **)b);
    })
  );

  puts("Input string for search.");
  fgets(str, sizeof(str), stdin);
  sscanf(str, "%s", target);

  search_result = (char **)bsearch(target, table, LENGTH(table), sizeof(char *),
    LAMBDA(int, (const void *restrict key, const void *restrict elm), {
      return strcmp((char *)key, *(char **)elm);
    })
  );
  if (search_result == NULL) {
    printf("'%s' was not found.\n", target);
  } else {
    printf("'%s' was found!!\n", target);
  }
  return EXIT_SUCCESS;
}