c++ fprintf prints only first string

Question

I tried with below code:

String hi = "hi";
String bye = "bye";
fprintf(fileout, "%d: %s, %s", 10, hi, bye); //fail 
fprintf(fileout, "%d: %s, %s", 10, "hi", "bye");//ok

however, this cannot write hi bye to the text file. What is wrong?

Paul Draper · Accepted Answer · 2014-02-10 05:54:10Z

5

fprintf and related functions are C functions.

You need a "C string", which is a null-terminated character array (char * or char const *), not a C++ string (std::string).

fprintf(fileout, "%d: %s, %s", 10, hi.c_str(), bye.c_str());

See fprintf and c_str().

Though C++ code will typically use the C++ I/O functions.

answered Feb 10, 2014 at 5:54

Paul Draper

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2 Comments

chwarr Over a year ago

Though, do note that the String that manhon is using is likely not std::string. Note that the capitalization differs. manhon, check whether your String class has a member function similar to std::string::c_str() and try using that.

Paul Draper Over a year ago

Yes, @c45207 makes a good point. Look for a function that returns char * (or const char * or char const *).

Jerry Coffin · Accepted Answer · 2014-02-10 05:56:57Z

0

You don't normally want to use fprintf and company in C++.

fileout << 10 << ": " << hi << ", " << bye;

answered Feb 10, 2014 at 5:56

Jerry Coffin

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2 Comments

manhon Over a year ago

I use fprintf becoz i am trying to write float numbers to file, some are round up to digit, some are round up to 2 decimal.

Jerry Coffin Over a year ago

@manhon: Then you'll want to look up std::setw and std::setprecision.

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