string_ext

A C++11, header-only implementation of sprintf with typechecking and error handling.

Implements printf http://www.cplusplus.com/reference/cstdio/printf/ style string formatting using C++ stringstreams and ios manipulators, returning the formatted result as a std::string.

Usage

Call to get a formatted string

str::format("...", args...)

Alternatively, call macro to pass along __LINE__ and __FILE__ for debugging

format_str("...", args...)

Equivalent to...
str::format(__LINE__, __FILE__, "...", args...)

Formats follow the form:

%[flags][width][.precision]specifier 

Use %% for a percent sign

flags	  : - (left align)
			+ (show sign)
			0 (pad with 0's)
			# (show base or decimal) 

specifier : d, i, u, o, x, X, n    (short/int/long/long long & unsigned variants)
			f, e, E, g, G		   (float / double / long double)
			s                      (string / any type with an ostream<< operator), 
			c                      (char), 
			p                      (ptr)
            b, B                   (bool)

Examples

Everything is just like it is with printf! But now you get error handling, typechecking, security, and dynamic memory which means no more buffer overruns!

/// Writing to stdout
printf("Hello %s.\n", "world");
// vs. 
std::cout << "Hello " << "world" << ".\n";
// vs.
std::cout << format_str("Hello %s.\n", "world");

---

/// Writing to stderr
int a = 42;
fprintf(stderr, "a = %d\n", a);
// vs. 
std::cerr << "a = " << a << "\n";
// vs.
std::cerr << format_str("a = %d\n", a);

---

/// Writing to a string buffer
char buf[256];
sprintf(buf, "a = %f b = %e c = %g\n", 1.234, 2.345, 3.456);
// vs.
std::ostringstream ss;
ss <<  "a = " << std::fixed			<< 1.234 
   << " b = " << std::scientific	<< 2.345 
   << " c = " << std::defaultfloat	<< 3.456 << "\n";
std::string buf = ss.str();
// vs.
std::string buf = format_str("a = %f b = %e c = %g\n", 1.234, 2.345, 3.456);

---

/// Print a struct or class object that has an ostream<< operator
struct SomeObject {
	int a;
	double d;

	/// The ostream operator can itself call format_str !
	friend std::ostream& operator<<(std::ostream& os, const Test &v) {
		os << format_str("SomeObject{ %i, %f }", v.a, v.d);
		return os;
	};
};
SomeObject obj{ 10, 3.14 };

printf("Here is an object: SomeObject{ %i, %f }\n", obj.a, obj.d);	// Have to look inside obj ourselves
// vs. 
std::cout << "Here is an object: " << obj << "\n";
// vs.
std::cout << format_str("Here is an object: %s\n", obj);

Error Handling

std::cout << format_str("Cause an error: %m", 0);

// Line: 100 File: 'test.cpp'
// String Format | Undefined format specifier : 'm'

std::cout << format_str("Cause an error: %i", 0.f);

// Line: 105 File: 'test.cpp'
// String Format | Incorrect format specifier for type (float): Saw 'i' | Expected 'f, e, E, g, G'

std::cout << format_str("Cause an error: %");

// Line: 110 File: 'test.cpp'
// String Format | Incomplete format string : Ended in '%'

std::cout << format_str("Cause an error: %d");

// Line: 115 File: 'test.cpp'
// String Format | Not enough arguments

std::cout << format_str("Cause an error: %*d", 0);

// Line: 251 File: 'test.cpp'
// String Format | Not enough arguments : Variable width needs '2' arguments. Have '1'

std::cout << format_str("Cause an error: %.*d", 0);

// Line: 256 File: 'test.cpp'
// String Format | Not enough arguments : Variable precision needs '2' arguments. Have '1'

std::cout << format_str("Cause an error: %*.*d", 0);

// Line: 251 File: 'test.cpp'
// String Format | Not enough arguments : Variable width & precision needs '3' arguments. Have '1'

std::cout << format_str("Cause an error: %*.*d", 0, 0);

// Line: 251 File: 'test.cpp'
// String Format | Not enough arguments : Variable width & precision needs '3' arguments. Have '2'

std::cout << format_str("Cause an error: %*d", 'a', 0);

// Line: 271 File: 'test.cpp'
// String Format | Invalid width argument : (char)

std::cout << format_str("Cause an error: %.*d", 3.14L, 0);

// Line: 276 File: 'test.cpp'
// String Format | Invalid precision argument : (long double)

std::cout << format_str("Cause an error: ", 1, 2, 3);

// Line: 120 File: 'test.cpp'
// String Format | Unused arguments : '3'

std::cout << format_str("Cause an error: %##d", 0);

// Line: 125 File: 'test.cpp'
// String Format | Format flag already set: 'Force Long'