This scale is also known as Ionian. These are simply different names of the same scale under different classification systems or musical traditions.
A heptatonic scale is a musical scale that has seven pitches per octave (Greek hepta = seven). A diatonic scale is a heptatonic scale that includes five whole steps and two half steps in each octave, and the two half steps are separated from each other by either two or three whole steps. In its strictest definition, a diatonic scale is one that may be derived from the pitches represented in successive white keys of the piano, or a transposition thereof. This would include the major scale, the natural minor scale and the descending form of the melodic minor (which is the same as the natural minor scale). This definition would exclude the ascending form of the melodic minor and the harmonic minor since they are not transpositions of the white-note pitches of the piano. However, in modern “inclusive” usage, all traditional major and minor scales are classified as diatonic; and StringMusic.info follows this convention.
C Major Scale for Guitar, Standard 6/12-String in Standard (EADGBE) Tuning