fprintf() prototype
int fprintf(FILE* stream, const char* format, ...);
The fprintf() function writes the string pointed to by format to the stream stream. The string format may contain format specifiers starting with % which are replaced by the values of variables that are passed to the fprintf() function as additional arguments.
It is defined in <cstdio> header file.
fprintf() Parameters
- stream: Pointer to an output file stream where the contents are written.
- format: Pointer to a null terminated string that is written to the file stream. It consists of characters along with optional format specifiers starting with %.
The format specifiers are replaced by the values of respective variables that follows the format string.
The format specifier has the following parts:
- A leading % sign
- Flags: Optional one or more flags that modifies the conversion behavior.
- - : Left justify the result within the field. By default it is right justified.
- + : The sign of the result is attached to the beginning of the value, even for positive results.
- Space: If there is no sign, a space is attached to the beginning of the result.
- # : An alternative form of the conversion is performed.
- 0 : It is used for integer and floating point number. Leading zeros are used to pad the numbers instead of space.
- Width: An optional * or integer value used to specify minimum width field.
- Precision : An optional field consisting of a . followed by * or integer or nothing to specify the precision.
- Length : An optional length modifier that specifies the size of the argument.
- Specifier: A conversion format specifier. The available format specifiers are as follows:
Format Specifier Description % Prints % c Writes a single character s Writes a character string d or i Converts a signed integer to decimal representation o Converts an unsigned integer to octal representation X or x Converts an unsigned integer to hexadecimal representation u Converts an unsigned integer to decimal representation F or f Converts floating-point number to the decimal representation E or e Converts floating-point number to the decimal exponent notation A or a Converts floating-point number to the hexadecimal exponent G or g Converts floating-point number to either decimal or decimal exponent notation n Returns the number of characters written so far by this call to the function. The result is written to the value pointed to by the argument p Writes an implementation defined character sequence defining a pointer. So the general format of format specifier is:
%[flags][width][.precision][length]specifier
- … : Other additional arguments specifying the data to be printed. They occur in a sequence according to the format specifier.
fprintf() Return value
If successful, the fprintf() function returns number of characters written. On failure it returns a negative value.
Example: How fprintf() function works
#include <cstdio>
int main()
{
FILE *fp;
fp = fopen("example.txt","w");
char lang[5][20] = {"C","C++","Java","Python","PHP"};
fprintf(fp,"Top 5 programming language\n");
for (int i=0; i<5; i++)
fprintf(fp, "%d. %s\n", i+1, lang[i]);
fclose(fp);
return 0;
}
When you run the program, a file "example.txt" will be created (if does not exist already) and it contains the following string:
Top 5 programming language 1. C 2. C++ 3. Java 4. Python 5. PHP
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