setvbuf() prototype
int setvbuf(FILE* stream, char* buffer, int mode, size_t size);
The setvbuf() function changes the buffering mode of the given file stream to the value of mode.
If the buffer is not null, the size of buffer is size, otherwise the function automatically allocates a buffer (based on value of size).
It is defined in <cstdio> header file.
setvbuf() Parameters
- stream: A file stream.
- buffer: Pointer to the buffer to be used by stream.
- mode: Buffering mode. The types of buffering modes are:
- _IOFBF: full buffering
- _IOLBF: line buffering
- _IONBF: no buffering
- size: The size of buffer in bytes.
setvbuf() Return value
The setvbuf() function returns zero on success and nonzero on failure.
Example: How setvbuf() function works
#include <iostream>
#include <cstdio>
#define SIZE 1024
using namespace std;
int main()
{
char buffer[SIZE] = "...";
char str[] = "This is first line\nThis is second line";
FILE *fp = fopen("test.txt","wb+");
/* no buffering, buffer remains unchanged */
setvbuf(fp,buffer,_IONBF,SIZE);
fwrite(str, sizeof(str), 1, fp);
cout << buffer << endl;
/* line buffering, only a single line is buffered */
setvbuf(fp,buffer,_IOLBF,SIZE);
fwrite(str, sizeof(str), 1, fp);
cout << buffer << endl;
/* full buffering, all the contents are buffered */
setvbuf(fp,buffer,_IOFBF,SIZE);
fwrite(str, sizeof(str), 1, fp);
cout << buffer << endl;
fclose(fp);
return 0;
}
When you run the program, the output will be:
... This is second line This is first line This is second line
