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Vugen: Replace Any String With Another

Here is an easy way to replace anything with anything in a captured string in your LoadRunner Vugen script. It is a function called “string_replace”. Place this in the top of your action section, right after the include but before the main section begins:

char *string_replace(char *input_string,
    char *substring_to_be_replaced,
    char *substitution_string)


// strstr function declaration
 char *strstr(const char *s1, const char *s2); 

// newstring variable the new string to be returned
// increase the buffer size if needed. Default is 200

char newstring[200]=""; 

// str is a temporary pointer to aid in creation of newstring;
// it points at the beginning of each substring that
// needs to be included in the new string.

char *str; 

// ptr is a pointer to hold strstr result.

char *ptr; 

str = input_string;

// search for substring_to_be_replaced and
// replace with substitution_string

 while((ptr = strstr(input_string, substring_to_be_replaced))!=NULL)
 input_string = &ptr[strlen(substring_to_be_replaced)];
 ptr[0] = '\0';
 strcat(newstring, str);
 strcat(newstring, substitution_string);
 str = input_string;

// concatenate the rest of the string

strcat(newstring, input_string);

return newstring;


Now here is an example of how this might be used. Let’s say you captured a string that had “&amp” in it and you need to replace them with simply a “&” character. You need to search the string and replace multiple occurrences. This is what it might look like in your action section:

lr_output_message("newstring: %s", lr_eval_string("{pNewString}"));
return 0;

Here is what the output/execution log might look like in Vugen with standard logging turned on:

Running Vuser…
Starting iteration 1.
Starting action Action.
Action.c(34): newstring: Value=RS=&;OI=&;LI=&;BD=20020107&;ED=99991231&;SQ=0&;XXXXX;
Ending action Action.
Ending iteration 1.
Ending Vuser…
Starting action vuser_end.
Ending action vuser_end.
Vuser Terminated.

Notice that this function saves the string as pInputString. This may be changed to dynamically pull a value from a web page with the web_reg_save_param() function too. Also, notice how string_replace() is used to scan, replace, and save the new string by being embedded in the lr_save_string() function. The lr_output_message() is totally optional. Instead you might actually use the {pNewString} parameter in your script where it is needed.

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