cpprestsdk fails parsing with backslash

Question

  wstring  str1 = L"\"address\":\"test \ 00001\",\"type\":\"Float\""
  wstring  str2 = L"\"address\":\"test \\ 00001\",\"type\":\"Float\""
  wstring  str3 = L"\"address\":\"test \\\ 00001\",\"type\":\"Float\""
  wstring  str4 = L"\"address\":\"test \\\\ 00001\",\"type\":\"Float\""

JSON parsing fails in first three cases and returns address=test \\ 0001 type=Float But I want only one backslash in address, How to resolve this issue?

Answer 1

I every language you need to escape certain characters within a string literal. In C++ the escape sequence starts with a \ and followed by an escaped value for the char to be represented.

In str1 = "\"address\":\"test \ 00001\",\"type\":\"Float\"" the \ (the one before 00001) is \040 (040 is for the white space space) which is an unknown escape sequence so this escape sequence is ignore, and will result in:

"address":"test \ 00001","type":"Float"

For str2 = "\"address\":\"test \\ 00001\",\"type\":\"Float\"" the \\ is a vlaid escape sequnce for \ and that results in: "address":"test \ 00001","type":"Float"

For str3 = "\"address\":\"test \\\ 00001\",\"type\":\"Float\"" the \ (the one before 00001) is the same as in the first case. And \\ before it is valid. So it results in:

"address":"test \\ 00001","type":"Float"

For str4 = "\"address\":\"test \\\\ 00001\",\"type\":\"Float\"" the escape squeence is correct and resutls in:

"address":"test \\ 00001","type":"Float"

This string is then once again pares by the JSON parse, there \ is also used as beginning of the escape sequence, so after parsing this resulting "address":"test \\ 00001","type":"Float", you will get "test \ 00001" for address.

That's one of the reasons why you don't want to build a JSON representation of data manually.