Read multiple line from std::can

I'm writing a unit test and I try to read some POST data from stdin, or cin. The data is like this:

callCount=1
page=/cs/admissions/admissions_tracker_result.jhtml?schoolId=436&classYear=2020
httpSessionId=xQIX_WS2vyua_JfEEKL0zAVRkxCLzMv-RM8ZJYuWfkaoA_IB6Ynn!788428762
scriptSessionId=5A7188C7ABF4B9F05D7CEB361E670361570
c0-scriptName=AdmissionScattergramService
c0-methodName=renderChart
c0-id=0
c0-e1=string:true
c0-e2=string:true
c0-e3=string:true
c0-e4=string:true
c0-e5=string:true
c0-e7=string:8
c0-e8=string:2
c0-e9=string:4
c0-e10=string:3
c0-e11=string:6
c0-e12=string:7
c0-e6=Array:[reference:c0-e7,reference:c0-e8,reference:c0-e9,reference:c0-e10,reference:c0-e11,reference:c0-e12]
c0-e13=string:true
c0-e14=string:true
c0-e15=string:true
c0-e16=string:true
c0-e17=string:true
c0-e18=string:true
c0-e19=string:true
c0-e20=string:true
c0-e22=string:1
c0-e23=string:2
c0-e24=string:3
c0-e25=string:4
c0-e26=string:0
c0-e21=Array:[reference:c0-e22,reference:c0-e23,reference:c0-e24,reference:c0-e25,reference:c0-e26]
c0-e27=string:true
c0-e28=string:true
c0-e30=string:AL
c0-e31=string:AK
c0-e32=string:AR
c0-e33=string:AS
c0-e34=string:AZ
c0-e35=string:CA
c0-e36=string:CO
c0-e37=string:CT
c0-e38=string:DC
c0-e39=string:DE

When I paste into the debugger, the program start runner automatically. I try to modify my code and use std::getline(std::can, post) instead of std::cin>>post; However, it didn't work. Here is the code:

 std::string url;
  std::string post;
  printf("enter the url\n");
  std::cin>>url;
  printf("enter the post data\n");
  std::string line;

    while (true) {
      getline(std::cin, line);
      if (line.empty()) {
        break;
      }
    post += '\n' + line;
    }

It seems like getline() is non-blocking. And the variable std::string post is just leave empty.