Ошибка isctype c

I encountered this assertion in the development of the project some time ago. After reading a lot of information on the Internet, there is still no result. Most of the processing methods are:

Set the project -> Configuration Properties -> C / C + ± > Language -> Default Char unsigned, select Yes (/J)

This operation changes the default char type in the project to unsigned char (unsigned char), but this method does not work in the current VS2010. The current VS2010 does not have this option, and I am not sure about the default char type of the project. Whether the change will have other effects on my project, so I did not use this method.

Debugging for a long time found that my program called isspace (determine whether the character is a space), isprint (determine whether it is a printed character), isalnum (determine whether the character is a number), isdigit function, these functions in isctype.c, by viewing Isctype.c implementation source code found:

	extern "C" int __cdecl _chvalidator(int const c, int const mask)
{
    _ASSERTE(c >= -1 && c <= 255);
    return _chvalidator_l(nullptr, c, mask);
}

extern "C" int __cdecl _chvalidator_l(_locale_t const locale, int const c, int const mask)
{
    _ASSERTE(c >= -1 && c <= 255);
    
    _LocaleUpdate locale_update(locale);

    int const index = (c >= -1 && c <= 255) ? c : -1;

    return locale_update.GetLocaleT()->locinfo->_public._locale_pctype[index] & mask; 
}

Since my project default char is a signed type, its value range is [-128 ~ 127], when the passed characters exceed 127 (may be Chinese), then the char type value overflows to a negative number, and when called When the function is reached, the assertion _ASSERTE(c> = -1 && c <= 255) is triggered.

Solution:
When calling these functions, the argument is first forced to an unsigned char type (value range 0~255)
eg: isprint((unsigned char) c);

I am working on writing a compiler for a school project, and this assignment calls for me to print the tokens of a text file to the console window. I want to make it clear I do not want my homework done for me.

I have been working with this stupid function that iterates through the file, and concatenates a char or a c-string value (my tutor was vague on this part of his instructions…) to a string variable named «token.» I can work through the first line of the file fine, which is «main()», but when I try and access the next line I get 1 of two errors. The first is a string subscript out of range error, though I think this was because I was trying to access part of a string array that didn’t exist. The most prevalent error I am getting is a debug assertion error:

Debug Assertion Failed Final.exe
File:f:ddvctoolscrt_bldself_x86crtsrcisctype.c Expression:
(unsigned)(c+1) <= 256

I have included my function and its associated header file. Nothing is going on in main except a function call. If at all possible, could you see what I am failing to see. I realize that my code structure is poor, I won’t lie (I am in school after all). So, any comments, criticism, and suggestions are very welcome. And always,thank you for any and all time.

.CPP File (As it is now)

    #include <iostream> 
    #include <string>

    using namespace std; 

    void tokenWork::openFile()
    {
        fileName = "test.txt"; 

        source.open(fileName);

        if(!source.is_open())
        {
       cout << "Cannot find file " << endl; 
        }
    }

    void tokenWork::traveseLine()
    {

    pos = 0; 
    while (!source.eof())
    {  
          getline(source,myLine); 
          int length = myLine.length(); 
          letters = new char[length];
          myLine.copy(letters,length); 

          c = letters[pos]; 

          if (isalpha(c))
             token = token + myLine[pos]; 
          else if (isdigit(c))
             token = token + letters; 
          else 
          {
             cout << token << endl; 
             token = ""; 
          }

          if (c == '{' || c == '}' || c == '+' || c == '=' || myLine[pos] == '(' || c == ')' || c == ';')
                cout << myLine[pos] << endl;  
          c = letters[pos++]; 
    }
}

.h file

    #ifndef H_LEX
    #define H_LEX

    #include <string> 
    #include <iostream> 
    #include <fstream> 

    using namespace std; 

    class tokenWork
    {
    public: 
    std::string fileName; 
    std::string myLine; 
    std::string token; 

    int pos; 
    int length; 
    int c;

    char *letters; 

    ifstream source; 

    void openFile(); 
    void traveseLine(); 
    void closeFile(); 

};

    #endif