Print a string with fprintf

Question

I am having an issue with printing a string which im using for debug purposes.

I create the string like so:

//checker is int 
std::stringstream buttonx; 
buttonx << "Button" << checker << "_x";

Now i try to print it to my error.txt file

FILE * p;
p = fopen ("error.txt","w");
fprintf(p, "%s" , buttonx.str());
fclose(p);

The output is:

,æ0

Its different every time. I'm not sure whats going on was hopeing some could explain the mistake?

Chris · Accepted Answer · 2012-11-14 06:57:48Z

7

fopen is plain C and cannot handle std::string. You need to input a char*, which you can access by calling .c_str() on the string, like this:

fprintf(p, "%s", buttonx.str().c_str());

answered Nov 14, 2012 at 6:57

Chris

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3 Comments

cHao Over a year ago

Or, use a std::ofstream as the C++ gods intended.

Sir Over a year ago

How would std::ofstream syntax look ?

cHao Over a year ago

@Dave: std::ofstream f("error.txt"); f << buttonx.str();. Or, if you're not writing anything else to the file, even std::ofstream("error.txt") << buttonx.str(); might work.

ShinTakezou · Accepted Answer · 2012-11-14 06:58:14Z

0

the function fprintf wants a null terminated string (a C string); you need the c_str() instead of yours:

 buttonx.c_str()

answered Nov 14, 2012 at 6:58

ShinTakezou

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