Question

所以我在处理文件ofstream和ifstream时陷入了一个编译器问题，我只是根本不知道这意味着什么...

开始吧。

我有以下课程：

class FS{
    public:
        string name;
        long long int size;
        long long int freeBlocks;
        long long int usedBlocks = 0;
        int blocksize = 128;
        vector<FS_File> file_list;
        char * ptr;                      //This is a malloc pointer
        void saveTo(ofstream& of); 
        void openFrom(ifstream& inf); 
    };

saveTo（） 函数中出现问题：

void FS::saveTo(ofstream& of){ 
  of.write(&name, sizeof(name)); 
  of.write(&size, sizeof(size));
  of.write(&freeBlocks, sizeof(freeBlocks)); 
  of.write(&usedBlocks, sizeof(usedBlocks)); 
  of.write(&blocksize, sizeof(blocksize)); 
  of.write(&file_list, sizeof(file_list));
  of.write((char *)&ptr, sizeof(ptr));
}

编译器给我下一个错误：

functions.cpp   In member function 'void FS::saveTo(std::ofstream&)':


    [Error] no matching function for call to 'std::basic_ofstream<char>::write(std::string*, long long unsigned int)'

    [Error] no matching function for call to 'std::basic_ofstream<char>::write(long long int*, long long unsigned int)'

    [Error] no matching function for call to 'std::basic_ofstream<char>::write(long long int*, long long unsigned int)'

    [Error] no matching function for call to 'std::basic_ofstream<char>::write(long long int*, long long unsigned int)'

    [Error] no matching function for call to 'std::basic_ofstream<char>::write(int*, long long unsigned int)'

    [Error] no matching function for call to 'std::basic_ofstream<char>::write(std::vector<FS_File>*, long long unsigned int)'

    [Error] no matching function for call to 'std::basic_ifstream<char>::read(std::string*, long long unsigned int)'

    [Error] no matching function for call to 'std::basic_ifstream<char>::read(long long int*, long long unsigned int)'

    [Error] no matching function for call to 'std::basic_ifstream<char>::read(long long int*, long long unsigned int)'

    [Error] no matching function for call to 'std::basic_ifstream<char>::read(long long int*, long long unsigned int)'

    [Error] no matching function for call to 'std::basic_ifstream<char>::read(int*, long long unsigned int)'

    [Error] no matching function for call to 'std::basic_ifstream<char>::read(std::vector<FS_File>*, long long unsigned int)'

每当我尝试调用下一个代码时：

ofstream outfile;
string filename = curFS.name + ".dat";
outfile.open(filename, ios::binary | ios::out);
curFS.save(outfile);
outfile.close();

我尝试了几件事，但是没有任何效果...

编译器错误是什么意思？我该如何解决？

Answer 1

错误消息不言自明。 std::ifstream和std::ofstream是char数据流，但是您正在尝试使用指向非char类型的指针来读取/写入数据。非write()指针的read()和char方法没有重载。

对于POD类型，您只需键入将指针指向char*的类型。

这不适用于非POD类型，例如std::string和std::vector。对于这些类型，您需要封送数据。

请尝试以下类似操作：

void FS::saveTo(ofstream& of)
{
    // std::string needs to be marshaled...
    size_t value = name.size();
    of.write(reinterpret_cast<char*>(&value), sizeof(value));
    of.write(name.c_str(), value);

    // POD types can be written as-is...
    of.write(reinterpret_cast<char*>(&size), sizeof(size));
    of.write(reinterpret_cast<char*>(&freeBlocks), sizeof(freeBlocks));
    of.write(reinterpret_cast<char*>(&usedBlocks), sizeof(usedBlocks));
    of.write(reinterpret_cast<char*>(&blocksize), sizeof(blocksize));

    // std::vector needs to be marshaled...
    value = file_list.size();
    of.write(reinterpret_cast<char*>(&value), sizeof(value));
    for (size_t i = 0; i < value; ++i) {
        // write file_list[i] to the stream as needed...
    }

    // dynamic data needs to be marshaled...
    value = strlen(ptr); // or whatever the actual allocated size is...
    of.write(reinterpret_cast<char*>(&value), sizeof(value));
    of.write(ptr, value);
}

void FS::openFrom(ifstream& inf)
{
    size_t value;

    // std::string needs to be marshaled...
    inf.read(reinterpret_cast<char*>(&value), sizeof(value));
    name.resize(value);
    inf.read(&name[0], value);

    // POD types can be read as-is...
    inf.read(reinterpret_cast<char*>(&size), sizeof(size));
    inf.read(reinterpret_cast<char*>(&freeBlocks), sizeof(freeBlocks));
    inf.read(reinterpret_cast<char*>(&usedBlocks), sizeof(usedBlocks));
    inf.read(reinterpret_cast<char*>(&blocksize), sizeof(blocksize));

    // std::vector needs to be marshaled...
    inf.read(reinterpret_cast<char*>(&value), sizeof(value));
    file_list.resize(value);
    for (size_t i = 0; i < value; ++i) {
        // read file_list[i] from stream as needed...
    }

    // dynamic data needs to be marshaled...
    inf.read(reinterpret_cast<char*>(&value), sizeof(value));
    free(ptr);
    ptr = (char*) malloc(value+1);
    inf.read(ptr, value);
    ptr[value] = '\0';
}

只需确保始终在启用std::ios_base::binary标志的情况下打开流。为了确保这一点，我建议将文件名而不是用户提供的流传递给saveTo() / openFrom()：

void FS::saveTo(const string& filename)
{
    ofstream outfile(filename, ios::binary);
    saveTo(outfile);
}

void FS::openFrom(const string& filename)
{
    ifstream infile(filename, ios::binary);
    openFrom(infile);
}

curFS.saveTo(curFS.name + ".dat");

curFS.openFrom(curFS.name + ".dat");

没有匹配的函数可用于调用'std :: basic_ofstream <char> :: write（std :: string *，long long unsigned int）'

1 个答案: