将字符串与 ifstream::getline 生成的字符串进行比较

发布于 2024-12-28 17:44:56 字数 848 浏览 5 评论 0原文

我正在开发一个项目，我需要读取 postscript 并解析文件中的数据以在我的程序中使用。我正在开发一个函数，通过确保后记具有开始和结束分隔符来测试后记是否有效。

下面是我为完成此任务而编写的代码段。我确信 postscript 文件中没有额外的空格或任何类似的内容会导致 delimitStr 和 lineStr 之间出现任何差异。我还尝试将 delimitStr 设置为“%%%BEGIN\0”和“%%%BEGIN”，但比较始终不起作用。

string lineStr;
bool beginFlag = false; //Switches to true when begin statement in postscript is found
string delimitStr = "%%%BEGIN"; //Starts as opening  delimiter. Switches to closing when opening is found.
while(psfile) {
    getline(psfile, lineStr);
    if(!beginFlag && lineStr == delimitStr) {
        beginFlag = true;
        delimitStr = "%%%END";
        cerr << "Begin found." << endl;
    }
    else if(beginFlag && lineStr == delimitStr)
        return true; //Only return true if file has beginning and ending delimiters.

任何帮助将不胜感激。

原文

I am working on a project where I need to read postscript and parse data from the file to use in my program. I am working on a function to test whether the postscript is valid by making sure it has opening and closing delimiters.

Below is the segment of code I have written to accomplish this. I am confident that there are no additional spaces or anything of the sort in the postscript file to cause any discrepancy between delimitStr and lineStr. I also attempted to set delimitStr to "%%%BEGIN\0" and "%%%BEGIN", but the comparison never works.

string lineStr;
bool beginFlag = false; //Switches to true when begin statement in postscript is found
string delimitStr = "%%%BEGIN"; //Starts as opening  delimiter. Switches to closing when opening is found.
while(psfile) {
    getline(psfile, lineStr);
    if(!beginFlag && lineStr == delimitStr) {
        beginFlag = true;
        delimitStr = "%%%END";
        cerr << "Begin found." << endl;
    }
    else if(beginFlag && lineStr == delimitStr)
        return true; //Only return true if file has beginning and ending delimiters.

Any help would be greatly appreciated.

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鯉魚旗 2025-01-04 17:44:56

将 delimitStr 更改为 delimitStr = "%%%BEGIN"; 因为 getline 会丢弃 '\n'
和
比较像 lineStr == delimitStr 这样的字符串。
不要将字符串与 c_str() 进行比较，因为它会返回 const char*。

显示差异的示例：

std::string s1("%%%BEGIN");
std::string s2("%%%BEGIN\n");
std::string s3("%%%BEGIN\0"); // Same as s1 because std::string stops at '\0'

std::cout << std::boolalpha << (s1 == s2) << '\n';      // Outputs: false
std::cout << (s1 == s3) << '\n';      // Outputs: true 
std::cout << (s2 == s3) << std::endl; // Outputs: false

Change delimitStr to delimitStr = "%%%BEGIN"; because getline discards the '\n'
and
compare strings like this lineStr == delimitStr.
DO NOT compare strings with c_str() as that returns a const char*.

Example showing the differences:

std::string s1("%%%BEGIN");
std::string s2("%%%BEGIN\n");
std::string s3("%%%BEGIN\0"); // Same as s1 because std::string stops at '\0'

std::cout << std::boolalpha << (s1 == s2) << '\n';      // Outputs: false
std::cout << (s1 == s3) << '\n';      // Outputs: true 
std::cout << (s2 == s3) << std::endl; // Outputs: false

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