Best way to extract numbers in the string?

[grancia]

Given following string having double quotes in input string, what is the best way to extract numbers only with nlohmann json?
input: "{'data_a': [1, 2], 'data_b': [3, 4]}"

[nickaein]

Have you read the examples? This will be pretty straightforward if the input is valid JSON string.

[grancia]

I have checked but it looks a bit different case.
For example, if json file looks like below how can we extract number from them? Meaning in case, the data's value is double quoted...
{"data": "{'data_a': [1, 2], 'data_b': [3, 4]}"}

[nickaein]

In this case your input is valid JSON string, but data field is a string containing {'data_a': [1, 2], 'data_b': [3, 4]}. The contents are not an valid JSON string as keys are single quoted. One approach to extract the number might be:

https://wandbox.org/permlink/DQ9FSnoaEELbwJhG

[grancia]

fixed! thank you!