C++ 对'；std：：流的基本单元<；char>；：：写入（std:：string*，long-long-unsigned-int）和#x27；

所以我在处理流文件和ifstream时遇到了一个编译器问题，我只是不知道这意味着什么

让我们开始吧

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); 
    };

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)'

我试过一些方法，但都不管用

编译器错误意味着什么？

---

如何解决此问题？

错误消息是不言自明的

std:：ifstream

和

std:：ofstream

是

char

数据流，但您正试图使用指向非

char

类型的指针读取/写入数据。非

char

指针的

write（）

和

read（）

方法没有重载

对于POD类型，您可以简单地将指针类型转换为

char*

这不适用于非POD类型，如

std:：string

和

std:：vector

。对于这些类型，您需要封送数据

请尝试类似以下内容：

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';
}

---

of.write（&name，sizeof（name））的作用与您想象的不同。按地址将
std:：string
写入文件流最终只会导致无意义的结果。按地址编写
std:：vector
对象也不是好兆头。按地址写
char*
也不会。只要想想在所有这些情况下，磁盘文件中实际写入了什么。而且，错误消息的意思正是他们所说的。请看合适的原型。您的by地址写入中有多少与该类型匹配。请记住，C++是强类型的。这确实是我的问题的解决方案，但有一个小问题。首先，我有一个问题。。。该sol是否读取openFrom函数中的信息并将其加载回类中？如果有：假设我创建了.dat文件并关闭了我用来创建该文件的程序。现在我打开另一个实例并告诉它打开.dat文件。它确实读取了文件，但当我试图访问它时，它根本没有任何信息。如果没有，我如何将信息加载回？对不起，我问了这么多问题，但这确实是我第一次使用它。@AlanMaldonado“这个sol是否读取openFrom函数中的信息并将其加载回类？”-是的。“它确实读取了文件，但当我试图访问它时，它根本没有任何信息”-那么您要么没有正确加载数据，要么调用了错误的
FS
对象上的
openFrom（）
，或者调用了无效对象。请编辑您的问题，以包括一个不适合您的问题。
ofstream outfile;
string filename = curFS.name + ".dat";
outfile.open(filename, ios::binary | ios::out);
curFS.save(outfile);
outfile.close();

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';
}

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");