c++ - 如何保存和恢复 std::istringstream 的缓冲区？

Question

我正在使用 istringstream 逐字读取 string。但是，当我的条件失败时，我需要能够将 istringstream 恢复到读取前一个单词之前。我的示例代码有效，但我想知道是否有更直接的方法来使用流来完成此操作。

std::string str("my string");
std::istringstream iss(str);

std::ostringstream ossBackup << iss.rdbuf(); // Writes contents of buffer and in the process changes the buffer
std::string strBackup(ossBackup.str());      // Buffer has been saved as string

iss.str(strBackup);                          // Use string to restore iss's buffer
iss.clear();                                 // Clear error states
iss >> word;                                 // Now that I have a backup read the 1st word ("my" was read)

// Revert the `istringstream` to before the previous word was read.
iss.str(strBackup);                         // Restore iss to before last word was read
iss.clear();                                // Clear error states
iss >> word;                                // "my" was read again

Answer 1

如果您愿意，您可以使用tellg() 和seekg() 来保存和恢复您的位置:

#include <string>
#include <sstream>

int main()
{
    std::istringstream iss("some text");

    std::string word;

    // save the position
    std::streampos pos = iss.tellg();

    // read a word
    if(iss >> word)
        std::cout << word << '\n';

    iss.clear(); // clear eof or other errors
    iss.seekg(pos); // move to saved position

    while(iss >> word)
        std::cout << word << '\n';

}