why string concatenation getting strange result in c++? -

i trying concatenate 2 strings in c++:

"g1-2" + "-%02d.jpg" 

and getting following result:

g1-2-1537817269.jpg 

why isn't result this: "g1-2-%02d.jpg"

wild guess!

you're printing concatenated string by

printf(str); 

where str "g1-2-%02d.jpg"

printf("g1-2-%02d.jpg");              ^^^^ //            but, corresponding integer in following? 

as can see there's %02d in string , printf seek integer argument. can not find , undefined behavior occurs. in best situation prints out random value string.

if guess true, try print string in form:

printf("%s",str); 

 

or use double % chis mentined:

"g1-2-%%02d.jpg"