Variable conversion in LoadRunner

In the last post, I have given an overview on what types of variables are seen in an LR Script and where they should be used.

This article covers on conversion of LR Variables to C Variables and viceversa.  There are three important LR functions used for the conversion. 
We'll  see one at a time.

lr_eval_string()
This function evaluates a load runner variable and returns its value if placed in flower braces. Let us try to understand how it really works.

lr_eval_string("test") returns a string called "test"
lr_eval_string("{test}") - Now this function checks if there is LoadRunner variable called test or not. 
If there is a LoadRunner variable named test and its value is "Welcome". Now the function lr_eval_string("{test}") returns a string "Welcome"

If no LoadRunner variable exists with the name test, then the function lr_eval_string("{test}") returns a string "{test}"

Now let us see two more last example of lr_eval_string() function:

Assumption: There is an LR variable called test whose value is "{Welcome}". There is another LR variable called Welcome whose value is "Performance Testing Online".

lr_eval_string("{test}") - This returns a string "{Welcome}"
lr_eval_string() function does not do nested evaluation

lr_eval_string(lr_eval_string("{test}"))
 = lr_eval_string("{Welcome}");
 = "Performance Testing Online"

LR to C String
Now that you understand the usage of lr_eval_string() function let us see how we can convert an LR Variable to C string variable.

char CStr[100];

to save "Performance Testing Online" into the string variable CStr, the syntax is:

strcpy(CStr, lr_eval_string(lr_eval_string("{test}")));

Please note that an equal symbol (=) cannot be used to assign a value to a string variable. We will have a separate article on why.

So, the conclusion is, to save an LR value to a C string variable, the lr_eval_string() function is used.

Now let us see, how we can convert an LR Parameter to C integer variable
 
let us assume that the LR variable test stores a value of "10".

LR to C Integers
This value should be converted to a string format first using lr_eval_string() function. This function returns a string value. To convert a string value into an integer, we have C function called atoi() read it as A to I (meaning alphabets to Integers)

int Count;

Count = atoi(lr_eval_string("{test}"));

This is how a value in LR variable is saved to a C variable. Though the heading says converting an LR variable to C variable, in fact we are storing the value of an LR variable into a C variable.

Now let us see the otherway i.e. converting a C integer / String to an LR parameter.

we have two functions named lr_save_string() and lr_save_int() to save a string and integer values to an LR parameter respectivily.

C to LR
int i = 256;

lr_save_int(i, "Total"); 

Now Total is an LR variable which stored a value of 256 in it. Inside the web_url() or web_submit_data or web_custom_request it can be used as {Total}

char Text[100] = "Welcome to Performance Testing Online";

lr_save_string(text, "Status");
Now Status is an LR variable which stored the entire string in it. In a web request it should be used as {Status}


I hope this article is informative and helpful.  If you have any questions, please feel free to comment.

Thanks,
Ram N