C++ c_str 不返回整个字符串

发布于 2024-08-07 06:41:15 字数 799 浏览 9 评论 0原文

我已经使用正常的 ifstream 和当前使用的 boost:iostream 尝试了以下代码，两者都有相同的结果。

它的目的是将文件从 physfs 加载到内存中，然后将其传递给处理程序进行处理（例如图像、音频或数据）。目前，当调用 c_str 时，它仅返回文件的一小部分。

        PhysFS::FileStream file("Resources/test.png" , PhysFS::OM_READ);

    if(file.is_open()) {

        String* theFile;

        theFile = new String((std::istreambuf_iterator<char>(file)), 
        std::istreambuf_iterator<char>());

        String::iterator it;
        for ( it=theFile->begin() ; it < theFile->end(); it++ ) {
            std::cout << *it; 
        } // Outputs the entire file

        std::cout << theFile->c_str(); // Outputs only the first few lines

    }

迭代器循环按预期输出整个 png 文件，但 c_str 调用仅返回前几个字符 (\211PNG)。

我已经尝试此代码的变体相当长一段时间但没有成功。有什么想法吗？

原文

I've tried the following code with both normal ifstreams and the current boost:iostream I'm using, both have the same result.

It is intended to load a file from physfs into memory then pass it to a handler to process (eg Image, audio or data). Currently when c_str is called it only returns a small part of the file.

        PhysFS::FileStream file("Resources/test.png" , PhysFS::OM_READ);

    if(file.is_open()) {

        String* theFile;

        theFile = new String((std::istreambuf_iterator<char>(file)), 
        std::istreambuf_iterator<char>());

        String::iterator it;
        for ( it=theFile->begin() ; it < theFile->end(); it++ ) {
            std::cout << *it; 
        } // Outputs the entire file

        std::cout << theFile->c_str(); // Outputs only the first few lines

    }

The iterator loop outputs the entire png file as expected, but the c_str call only returns the first few characters (\211PNG).

I've been trying variations of this code for quite some time with no success. Any ideas?

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明天过后 2024-08-14 06:41:15

我想象下一个字符是空（ASCII 0）字节。 c_str() 只是给你一个 *char，因此你对 stdout 的写入被解释为以第一个空字节结尾的 C 类字符串。

如果您确实需要该字符串的类似 C 的接口，那么最主要的是 theFile->c_str() 指向您的数据，而 theFile.length 为您提供字符串中的字符数。所以你可能想做这样的事情：

char *c_value = theFile->c_str()
for (int i = 0; i < theFile.length; i++)
{
   cout << c_value[i];
}

真正的解决方案取决于你为什么要首先转换为 char * 。如果您调用仅接受 char * 的旧函数，则该旧函数可能还有一个长度参数。

I imagine that the next character is a null (ASCII 0) byte. c_str() simply gives you a *char, therefore your write to stdout is interpreted as a class C string which ends at the first null byte.

If you really need a C-like interface to this string, the main thing is that theFile->c_str() points to your data and theFile.length gives you the number of characters in the string. So you might want to do something like this:

char *c_value = theFile->c_str()
for (int i = 0; i < theFile.length; i++)
{
   cout << c_value[i];
}

The real solution depends on why you are converting to a char * in the first place. If you are calling a legacy function that only accepts char *, there is likely also a length argument to that legacy function.

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