Getting a (const char*) representation of an integer in a one-liner

Question

I'm working on a software using a home-made report library which takes only (const char *) type as an argument :

ReportInfo(const char* information);
ReportError(const char* error);
[...]

As I'm trying to report value of integers, I'd like to get a representation of those integers in a const char* type. I can do it that way :

int value = 42;
string temp_value = to_string(value);
const char *final_value= temp_value.c_str();
ReportInfo(final_value);

It would be great if I could do it without instancing the temp_value. I tried this :

int value = 42;
const char* final_value = to_string(value).c_str();
ReportInfo(final_value);

but final_value is equal to '\0' in that case.

Any idea how to do it ?

I don't get the line "but final_value is egal to '\0' in that case." — David Haim, Aug 05 '15 at 09:11
Is there a shortage of newline characters in your work environment? Can you not spare the piddlingly small amount of memory needed for `temp_value`? :-) — paxdiablo, Aug 05 '15 at 09:12
Worth reading too: http://stackoverflow.com/questions/10006891/stdstringc-str-and-temporaries — deviantfan, Aug 05 '15 at 09:27
@DavidHaim When I debug this part of my code, i can see that the value in `final_value`is '\0'. It doesn't make sense to me. — augustin-r, Aug 05 '15 at 09:31
@augustin-r Because undefined behaviour doesn´t make sense. It´s a dangling pointer, nothing less or more. — deviantfan, Aug 05 '15 at 09:35
@deviantfan ok. makes sense now. sry about that, i'm really new to programming :) — augustin-r, Aug 05 '15 at 09:38

score 6 · Accepted Answer · answered Aug 05 '15 at 09:15

6

You could try

ReportInfo(to_string(value).c_str());

because the temporary will not be destroyed until ReportInfo returns.

answered Aug 05 '15 at 09:15

alain

score 4 · Answer 2 · answered Aug 05 '15 at 09:12

4

to_string(value) returns a temporary, so in your second example its lifetime ends at the end of the expression. so you have dangling pointer.

answered Aug 05 '15 at 09:12

Jarod42

2 Answers2