如何使用RapidJSON将压缩后的JSON结果存储到C++ string而非输出到stdout

Both of your questions—capturing compressed JSON output and redirecting parser output to a string—share the same core solution in RapidJSON: swap out the FileWriteStream (which writes to stdout/files) with RapidJSON's StringBuffer to capture output in memory, then convert that buffer to a C++ std::string. Here's how to adjust your example code:

Modified Example Code #

#include "rapidjson/reader.h"
#include "rapidjson/writer.h"
#include "rapidjson/filereadstream.h"
#include "rapidjson/stringbuffer.h"  // Add this header for in-memory buffer
#include "rapidjson/error/en.h"
#include <string>  // For std::string support
using namespace rapidjson;

int main() {
    // --- Original input setup (reading from stdin) ---
    char readBuffer[65536];
    FILE* fp = stdin;
    FileReadStream is(fp, readBuffer, sizeof(readBuffer));

    // --- Replace FileWriteStream with StringBuffer ---
    StringBuffer outputBuffer;  // Stores output in memory instead of stdout
    Writer<StringBuffer> writer(outputBuffer);  // Attach writer to the in-memory buffer

    // --- Parse and process (same logic, but output goes to buffer) ---
    Reader reader;
    if (!reader.Parse(is, writer)) {
        fprintf(stderr, "\nError(%u): %s\n", static_cast<unsigned>(reader.GetErrorOffset()), GetParseError_En(reader.GetParseErrorCode()));
        return 1;
    }

    // --- Convert StringBuffer to C++ std::string ---
    std::string compressedJson(outputBuffer.GetString(), outputBuffer.GetSize());

    // Now you can use 'compressedJson' for storage, processing, etc.
    // Optional: Verify the result by printing it
    printf("Compressed JSON stored in string:\n%s\n", compressedJson.c_str());

    return 0;
}

Key Changes Explained #

• Add StringBuffer header: Include <rapidjson/stringbuffer.h> to access RapidJSON's in-memory output buffer.
• Replace FileWriteStream: Instead of writing directly to stdout, we use StringBuffer to hold the processed JSON data in RAM.
• Convert to std::string: Use outputBuffer.GetString() (returns a null-terminated const char*) and outputBuffer.GetSize() to safely initialize a C++ string.

For DOM-Based Workflows #

If you're using a parsed Document instead of the direct Reader/Writer pipeline, the same approach works to serialize the DOM to a string:

// Assume you have a populated rapidjson::Document doc
StringBuffer buffer;
Writer<StringBuffer> writer(buffer);
doc.Accept(writer);

std::string jsonString(buffer.GetString(), buffer.GetSize());

This method handles both compressed (whitespace-free) JSON output and any other parser/writer output you want to capture in a string instead of printing to stdout.

内容的提问来源于stack exchange，提问作者HarshGiri