如何读取json格式文本的字符流

Question

I am dealing with a sub-process (created using fork/exec -- aka the child ) that outputs on its std-out some json formatted text.

I have a pipe between the parent and child process, where the parent is reading the child std-out a character at a time (using getc ).

The parent is not using the blocking waitpid function but keeps checking the io pipe for any characters in it.

-- Up to here everything is implemented and functional --

I am using a json c++ library that can be used to read json files.

But obviously a half written json file can't be read; And since the parent is reading from the child a character at a time, how can it keep track of the characters until the first valid json object is detected and so on?

Please let me know if I am not clear so I try to rephrase.

Answer 1

If your parser does not support streaming, consider another library.

yajl is an ANSI-C parser for streaming JSON, it should work with your C++ code.

There are a bunch of other C and C++ tools listed at the bottom of the json.org homepage. One of them might work even better.

Answer 2

"First valid json object" is troubling. JSON only permits one top-level object, so you should be able to just read until EOF (assuming you've closed your pipes properly).