fprintf behaviour

I use IGOR to group and sort EDS spectra (counts vs. energy) which I then want to export and quantify in external software. The latter needs to read a header from a spectrum to identify instrument settings. I load this header from an existing spectrum and store it as a global string variable. The string header may look like this (print header):

•print header
#FORMAT : EMSA/MAS Spectral Data File
#VERSION : 1.0
#TITLE : Base(1)
#DATE : 20-SEP-2013
#TIME : 13:55: 6
#NPOINTS : 2048
#YUNITS : Intensity
#XPERCHAN : 0.010000000
#OFFSET : 0.000000000
#CHOFFSET : 0.000000
#XLABEL : X-Ray Energy
#YLABEL : X-Ray Intensity
#BEAMKV -kV: 15.0
#EMISSION -uA: 0.0000
#PROBECUR -nA: 1.0000
#BEAMDIAM -nm: 0.0
#MAGCAM : 0.0
. //more lines to follow


After the last entry "#SPECTRUM :" the actual data would follow. The header in this particular case contains about 540 entries (lines). My export function looks like:

function ExportSpectrum(header, spectrum)
    string header
    wave spectrum
    Variable refnum
    string filename = NameOfWave(spectrum)
    Duplicate/O/Free  spectrum Energy
    Energy = x
    Open/Z=2 /P = SpectrumPath /T="emsa"  refnum   as FileName+".emsa"          // path exists from loading header
    if (V_flag == -1)   //User cancelled dialog
        return -1
    fprintf refnum, Header                                          // writes header file to file, followed by return
    wfprintf refnum, "%g, %12d,\r\n",  Energy, spectrum         // writes energy and count data to file, followed by return
    fprintf refnum, "#ENDOFDATA   : \r\n"
    Close refnum
    return 1

The problem is that fprintf refnum header does not write the header completely to file (same for fprintf 1 header and the history window) but a large portion of the string is missing. Would that be for some reason an expected behaviour?

I would not be shocked to discover that fprintf is printing into a fixed-sized buffer. Try printing the header using Fbinwrite then print the remainder with a separate fprintf call.
--Jim Prouty
Software Engineer, WaveMetrics, Inc.
FBinWrite worked but in the end I changed my header load procedure that now creates a header text wave instead of a string.