:orphan:
# PetscVFPrintf
All PETSc standard out and error messages are sent through this function; so, in theory, this can can be replaced with something that does not simply write to a file. 
## Synopsis
```
PetscErrorCode PetscVFPrintfDefault(FILE *fd, const char *format, va_list Argp)
```
To use, write your own function for example,
```none
   PetscErrorCode mypetscvfprintf(FILE *fd, const char format[], va_list Argp)
   {
     PetscErrorCode ierr;

     PetscFunctionBegin;
      if (fd != stdout && fd != stderr) {  handle regular files
         CHKERR(PetscVFPrintfDefault(fd,format,Argp));
     } else {
        char   buff[BIG];
        size_t length;
        PetscCall(PetscVSNPrintf(buff,BIG,format,&length,Argp));
        now send buff to whatever stream or whatever you want
    }
    PetscFunctionReturn(PETSC_SUCCESS);
   }
```

then before the call to `PetscInitialize()` do the assignment `PetscVFPrintf = mypetscvfprintf`;




## Note
For error messages this may be called by any MPI process, for regular standard out it is
called only by MPI rank 0 of a given communicator


## Developer Note
This could be called by an error handler, if that happens then a recursion of the error handler may occur
and a resulting crash


## See Also
 `PetscVSNPrintf()`, `PetscErrorPrintf()`, `PetscFFlush()`

## Level
developer

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/sys/fileio/mprint.c.html#PetscVFPrintf">src/sys/fileio/mprint.c</A>


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[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/src/sys/fileio/mprint.c)


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