strngs.h

/**********************************************************************
 * File:        strngs.h  (Formerly strings.h)
 * Description: STRING class definition.
 * Author:      Ray Smith
 * Created:     Fri Feb 15 09:15:01 GMT 1991
 *
 * (C) Copyright 1991, Hewlett-Packard Ltd.
 ** Licensed under the Apache License, Version 2.0 (the "License");
 ** you may not use this file except in compliance with the License.
 ** You may obtain a copy of the License at
 ** http://www.apache.org/licenses/LICENSE-2.0
 ** Unless required by applicable law or agreed to in writing, software
 ** distributed under the License is distributed on an "AS IS" BASIS,
 ** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 ** See the License for the specific language governing permissions and
 ** limitations under the License.
 *
 **********************************************************************/

#ifndef STRNGS_H
#define STRNGS_H

#include <cassert>      // for assert
#include <cstdint>      // for uint32_t
#include <cstdio>       // for FILE
#include <cstring>      // for strncpy
#include "platform.h"   // for TESS_API

namespace tesseract {
class TFile;
}  // namespace tesseract.

// STRING_IS_PROTECTED means that  string[index] = X is invalid
// because you have to go through strings interface to modify it.
// This allows the string to ensure internal integrity and maintain
// its own string length. Unfortunately this is not possible because
// STRINGS are used as direct-manipulation data buffers for things
// like length arrays and many places cast away the const on string()
// to mutate the string. Turning this off means that internally we
// cannot assume we know the strlen.
#define STRING_IS_PROTECTED  0

template <typename T> class GenericVector;

class TESS_API STRING
{
  public:
    STRING();
    STRING(const STRING &string);
    STRING(const char *string);
    STRING(const char *data, int length);
    ~STRING();

    // Writes to the given file. Returns false in case of error.
    bool Serialize(FILE* fp) const;
    // Reads from the given file. Returns false in case of error.
    // If swap is true, assumes a big/little-endian swap is needed.
    bool DeSerialize(bool swap, FILE* fp);
    // Writes to the given file. Returns false in case of error.
    bool Serialize(tesseract::TFile* fp) const;
    // Reads from the given file. Returns false in case of error.
    // If swap is true, assumes a big/little-endian swap is needed.
    bool DeSerialize(tesseract::TFile* fp);
    // As DeSerialize, but only seeks past the data - hence a static method.
    static bool SkipDeSerialize(tesseract::TFile* fp);

    bool contains(const char c) const;
    int32_t length() const;
    int32_t size() const { return length(); }
    // Workaround to avoid g++ -Wsign-compare warnings.
    uint32_t unsigned_size() const {
      const int32_t len = length();
      assert(0 <= len);
      return static_cast<uint32_t>(len);
    }
    const char *string() const;
    const char *c_str() const;

    inline char* strdup() const {
     int32_t len = length() + 1;
     return strncpy(new char[len], GetCStr(), len);
    }

#if STRING_IS_PROTECTED
    const char &operator[] (int32_t index) const;
    // len is number of chars in s to insert starting at index in this string
    void insert_range(int32_t index, const char*s, int len);
    void erase_range(int32_t index, int len);
#else
    char &operator[] (int32_t index) const;
#endif
    void split(const char c, GenericVector<STRING> *splited);
    void truncate_at(int32_t index);

    bool operator== (const STRING & string) const;
    bool operator!= (const STRING & string) const;
    bool operator!= (const char *string) const;

    STRING & operator= (const char *string);
    STRING & operator= (const STRING & string);

    STRING operator+ (const STRING & string) const;
    STRING operator+ (const char ch) const;

    STRING & operator+= (const char *string);
    STRING & operator+= (const STRING & string);
    STRING & operator+= (const char ch);

    // Assignment for strings which are not null-terminated.
    void assign(const char *cstr, int len);

    // Appends the given string and int (as a %d) to this.
    // += cannot be used for ints as there as a char += operator that would
    // be ambiguous, and ints usually need a string before or between them
    // anyway.
    void add_str_int(const char* str, int number);
    // Appends the given string and double (as a %.8g) to this.
    void add_str_double(const char* str, double number);

    // ensure capacity but keep pointer encapsulated
    inline void ensure(int32_t min_capacity) { ensure_cstr(min_capacity); }

  private:
    typedef struct STRING_HEADER {
      // How much space was allocated in the string buffer for char data.
      int capacity_;

      // used_ is how much of the capacity is currently being used,
      // including a '\0' terminator.
      //
      // If used_ is 0 then string is nullptr (not even the '\0')
      // else if used_ > 0 then it is strlen() + 1 (because it includes '\0')
      // else strlen is >= 0 (not nullptr) but needs to be computed.
      //      this condition is set when encapsulation is violated because
      //      an API returned a mutable string.
      //
      // capacity_ - used_ = excess capacity that the string can grow
      //                     without reallocating
      mutable int used_;
    } STRING_HEADER;

    // To preserve the behavior of the old serialization, we only have space
    // for one pointer in this structure. So we are embedding a data structure
    // at the start of the storage that will hold additional state variables,
    // then storing the actual string contents immediately after.
    STRING_HEADER* data_;

    // returns the header part of the storage
    inline STRING_HEADER* GetHeader() {
      return data_;
    }
    inline const STRING_HEADER* GetHeader() const {
      return data_;
    }

    // returns the string data part of storage
    inline char* GetCStr() { return ((char*)data_) + sizeof(STRING_HEADER); }

    inline const char* GetCStr() const {
      return ((const char *)data_) + sizeof(STRING_HEADER);
    }
    inline bool InvariantOk() const {
#if STRING_IS_PROTECTED
      return (GetHeader()->used_ == 0) ?
        (string() == nullptr) : (GetHeader()->used_ == (strlen(string()) + 1));
#else
      return true;
#endif
    }

    // Ensure string has requested capacity as optimization
    // to avoid unnecessary reallocations.
    // The return value is a cstr buffer with at least requested capacity
    char* ensure_cstr(int32_t min_capacity);

    void FixHeader() const;  // make used_ non-negative, even if const

    char* AllocData(int used, int capacity);
    void DiscardData();
};
#endif