Understanding C++ Printf Function With Examples

The C++ Printf Prototype

The C++ printf prototype is:

int printf(const char * format, ...);

The printf prototype is defined in the <cstdio> header file. When you use the printf() function, it prints the string pointed out by the format to the standard output stdout. The format can also contain some specifiers that start with a % and replace values of variables with the printf() function. To put it simply, they work as additional arguments to the printf() function.

The C++ Printf Parameters

The C++ prototype contains the following parameters:

• const char: Any text to be printed on the console as is
• format: A pointer to the string with the optional format specifier starting with the %d sign.

Return Value of Printf in C++

C++ printf returns:

• The number of characters written if successful
• A negative value, if failed

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General Form of Format Specifier

The general form of a C++ printf format specifier is as below:

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

In the above format:

• %: This is the leading sign that denotes the beginning of the format specifier
• Flags: An optional one or more values that modifies the conversion behavior. The available values are:
• -: The result of printf function is by default right justified. This value left justifies the results
• +: This will add a sign to the values of the result, even for the positive values
• Space: If there is no sign attached to a value, this will attach a space to the beginning of the result
• #: This leads to an alternative form of conversion being performed
• 0: You use this flag for integers and floating-point numbers to pad the values with zeros instead of space
• Width: An optional field that accepts * or an integer value to determine the minimum width field
• Precision: An optional argument specifies precision by accepting a *, integer value, or nothing after a ‘.’ symbol
• Length: An optional parameter that defines the size of the argument
• Specifier: This field accepts a conversion format specifier

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Format Specifiers Used in C++ Printf

Printf in C++ can accept the following format specifiers.

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Examples of C++ Printf() Function

Now that you know the fundamentals of C++ printf, look at some examples that will give you a better understanding of how the printf() function in C++ works.

Example 1

In this example, you will simply display the value of an integer using %d and write a string to stdout using the %s format specifiers.

#include <cstdio>

int main(){

    int i = 9;

    char name[] = "Simplilearn";

    printf("i = %d \n", i);

    printf("Welcome to %s \n", name);    

    return 0;

}

Output:

Example 2

In this example, you will use various format specifiers from the above table to define the conversion behavior and get the result in the desired format.

#include <cstdio>

int main(){

    char c = 'S';

    float x = 7.0, y = 9.0;

    double d = 6.548;

    int i = 50;

    printf("The float division is : %.3f / %.3f = %.3f \n", x,y,x/y);

    printf("The double value is : %.4f \n", d);

    printf("Setting the width of c : %*c \n",3,c);

    printf("The octal equivalent of %d is %o \n",i,i);

    printf("The hex equivalent of %d is %x \n",i,i);

    return 0;

}

Output:

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C++ Printf Vs. Sprintf

The Sprintf() function in C++ is almost similar to the printf() function with a single major difference. While the C++ printf writes to the standard output, the sprintf writes the output to a string buffer. The sprintf() function prototype is:

int sprintf(char * buffer, const char * format, ...);

In the above prototype, the parameters are:

• Buffer: Pointer to a buffer where the results will be written
• Format: Pointer to a null-terminated string written to the file stream

Example of C++ Stringf() Function

In the below example, you will write a string to a buffer using the sprintf function and output the formatted string. You will also display the total number of characters written to the buffer.

#include <cstdio>

#include <iostream>

using namespace std;

int main(){

    char buf[100];

    int return_Val;

    char my_name[] = "Simplilearn";

    char topic[] = "tutorials";

    return_Val = sprintf(buf, "Welcome to %s you can read various programming %s here!!", my_name, topic);

    cout << buf << endl;

    cout << "Total characters written are: " << return_Val << endl;

    return 0;

}

Output:

Printf Vs. Cout in C++

The C++ printf() function is usually used in C programming but can also run in C++. However, the cout is specifically an addition in C++. The table below displays the significant differences between the C++ printf and cout.

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Example of C++ Cout

In the example below, you will see the use of C++ printf and cout simultaneously to see the difference.

#include <iostream>

using namespace std;

int main() {

   char c = 'S';

   cout<< "The value of c : " << c;

   printf("\nThe value of c : %c", c);  

   return 0;

}

Output:

Conclusion

You learned everything about the C++ printf() function in this article. You have also seen different format specifiers that you can use to format the results and use them in examples. Now it's time to use the other specifiers too. If you want to learn more such fundamental concepts of C++ programming, you can refer to Simplilearn's C++ Tutorial for Beginners. The tutorial is designed for beginners and covers all the basic concepts in detail. 

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