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这些天我一直在为 CHIP-8 制作汇编程序，今天我尝试实现参数以使操作码正常工作。但是，当我必须编写 2 个参数来完成操作码时，我有以下代码：

// Chip8Instruction is a struct I've made that holds the final machine code to be written, the mnemonic,
// the argument count and the position for each argument in hex
void writeTwoArguments(Chip8Instruction instruction, const std::string& line, int lineNum, const std::string& romName) {
    unsigned int arg1;
    unsigned int arg2;
    
    std::string remainingLine = line;
    std::string testStr;

    std::stringstream stringStream;


    // Arguments are comma and then space separated, assume I give 3, FF
    std::string::size_type commaPos = line.find(',');
    
    if (commaPos != std::string::npos) {
        stringStream << std::hex << remainingLine.substr(0, commaPos); // This writes 3, like it should
        testStr = stringStream.str(); // Holds "3", like it should
        stringStream >> arg1; // This holds 0x3, like it should
        stringStream.str("");

        remainingLine.erase(0, commaPos+2); // FF remains, like it should
        stringStream << std::hex << remainingLine;
        testStr = stringStream.str(); // This holds nothing but it should have "FF", if I don't empty the stream it holds "3" from before
        stringStream >> arg2; // This also holds nothing but it should have 0xFF, holds 0x3 if not empty stream

        instruction.machineCode = instruction.start + (arg1 * instruction.arg1Pos) + (arg2 * instruction.arg2Pos);
    }

    writeMultipleDigitsToROM(romName, instruction.machineCode, lineNum);

}

最小可重现示例：

#include <iostream>
#include <sstream>

int main() {
   std::string line = "3, FF";

   std::stringstream stringStream;

   unsigned int int1;
   unsigned int int2;

   // Get position of comma
   std::string::size_type commaPos = line.find(',');

   // Get everything up to the comma
   stringStream << std::hex << line.substr(0, commaPos);
   stringStream >> int1; // This holds 0x3, like it should
   stringStream.str(""); 
   line.erase(0, commaPos+2); // "FF" remains, like it should
   stringStream << std::hex << line;
   stringStream >> int2; // This is empty but should be 0xFF
   
}

正如代码注释所描述的，所持有的值要么是错误的，要么是过时的。可能是什么问题，为什么以及如何解决？

感谢所有帮助，谢谢！

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2 回答 2

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我尝试用这段代码隔离问题：

#include <iostream>
#include <string>
#include <sstream>

using namespace std;

int main() {
    string input = "3, FF";
    stringstream ss;
    ss << input.substr(0, 1);
    cout << ss.str() << endl;
    input.erase(0, 3);
    ss.str("");
    cout << input << endl;
    ss << std::hex << input;
    cout << ss.str() << endl;

    return 0;
}

但是，它似乎对我来说可以正常工作。不知道有什么区别，抱歉，除非我输入格式有误。顺便说一句，我建议不要提取到字符串流，而是通过将输入包装在字符串流中来从中提取，如下所示：

int arg1, arg2;
string comma;
stringstream ss(input);
ss >> std::hex >> arg1 >> comma >> arg2;
cout << arg1 << endl;
cout << arg2 << endl;

更好的是，您可以为您的类型重载流提取运算符operator>>，所以它可能是这样的：

Chip8Instruction c;
ss >> c;
// do stuff now that c is filled in

您可以通过声明如下内容来做到这一点：

istream& operator>>(istream& in, Chip8Instruction& out) {
   // where your code to parse the string could go
}

抱歉，我无法解决实际的解析问题，但我不清楚我所做的与你不同。

于 2021-02-17T11:39:20.807 回答
2

第一：std::hex改变整数的打印或扫描方式。它对line-line是一个字符串没有影响。stringStream << std::hex << line;是一样的stringStream << line;。

完成后，stringStream >> int1;将eof在内部设置位stringStream。要扫描其他任何内容，您必须先清除它。请研究如何重置stringstream.

要读取hex数字，您必须告诉您的流您要读取十六进制数字。F不是数字！

但总体而言，用法很奇怪 - 只需从中读取内容，stringstream它实际上就是从中读取数据的内容。忘记你的string工作stream。记得处理错误。我能看见：

#include <iostream>
#include <sstream>
#include <iomanip>

int main() {
    std::string line = "3, FF";

    std::istringstream ss(line);
    unsigned int int1;
    unsigned int int2;
    if (!(
            (ss >> std::dec >> int1) &&
            ss.get() == ',' &&
            (ss >> std::hex >> int2)
            )) {
        std::cerr << "read failed\n";
        abort();
    }
    std::cout << int1 << " " << int2 << "\n";
}
于 2021-02-17T12:08:30.453 回答