Here are the data structures with brief descriptions:

C_amatrix	Representation of a matrix as an array in column-major order
C_avector
C_bem2d	Main container object for computation of BEM related matrices and vectors
C_bem3d	Main container object for computation of BEM related matrices and vectors
C_bem3d_ocl	This structure contains geometry information for the OpenCL computation aswell as all OpenCL kernels and buffers for transferring work packages between main memory and GPU memory
C_block	Representation of block trees
C_blockentry	Auxiliary structure for hierarchical iterators for a block cluster tree
C_cluster	Representation of cluster trees
C_clusterbasis	Representation of a cluster basis
C_clustergeometry	Representation of a clustergeometry object
C_clusteroperator	Representation of a cluster operator
C_curve2d	Representation of a polygon in 2D
C_dblock	Directional block tree
C_dcluster	Directional cluster tree
C_dclusterbasis	Representation of a directional cluster basis
C_dclusteroperator	Representation of a directional cluster operator
C_dh2matrix	Tree structure representing a $\mathcal{DH}^2$ -matrix
C_diradmdata	Data for directional admissibility condition
C_duniform	Uniform matrices with directional cluster bases
C_h2matrix	Representation of $\mathcal{H}^2$ -matrices
C_h2matrixlist	List of h2matrix objects
C_haccum	Accumulator for H-matrix products
C_helmholtz_data	Simple struct that containts the wavevector $\vec \kappa$ and some source point
C_hmatrix	Representation of $\mathcal{H}$ -matrices
C_kernelbem2d	Substructure containing callback functions to different types of kernel evaluations
C_kernelbem3d	Substructure containing callback functions to different types of kernel evaluations
C_leveldir	Families of directions for all levels of the cluster tree
C_listnode	Simple singly linked list to store unsigned inter values
C_macrosurface3d	Representation of a parametrized surface
C_merge_data_nf	Struct to store input data for multiple calls to nearfield integration routine
C_nearfield_args	Struct to store the parameters of the nearfield integration routine
C_ocl	Structure that contains basic OpenCL objects for arbitrary computations
C_op_callbacks	Struct of callback functions for different quadrature cases that arise in the nearfield computation
C_patentry	Representation of one non-zero entry in a sparsepattern
C_realavector
C_rkmatrix	Representation of a low-rank matrix in factorized form
C_singquad1d	This struct collects all type of quadrature formulas needed by the computation of matrix entries within BEM
C_singquad2d	This struct collects all type of quadrature formulas needed by the computation of matrix entries within BEM
C_sparsematrix	Representation of a sparse matrix in compressed row format
C_sparsepattern	Representation of the sparsity pattern of a matrix
C_surface3d	Representation of a triangle surface mesh
C_task	Simple representation of a task
C_taskgroup	A collection of tasks for the same callback function
C_tet3d	Representation of a three-dimensional tetrahedral mesh
C_tet3dp1	Representation of a trial space with piecewise linear nodal basis functions on a three-dimensional tetrahedral mesh
C_tet3dref	Representation of the refinement relationship between two meshes
C_tet3drt0	Representation of a trial space with lowest order Raviart-Thomas basis functions on a three-dimensional tetrahedral mesh
C_tri2d	Representation of a two-dimensional triangular mesh
C_tri2dp1	Representation of a trial space with piecewise linear nodal basis functions on a two-dimensional triangular mesh
C_tri2dref	Representation of the refinement relationship between two meshes
C_tri2drt0	Representation of a trial space with lowest order Raviart-Thomas basis functions on a two-dimensional triangular mesh
C_tri_list	Simple singly connected list to efficiently store a list of triangles
C_tridiag	Real tridiagonal matrix , represented by vectors containing the diagonal, sub- and superdiagonal
C_truncblock	Description of basis and weights for one submatrix in the unification algorithm
C_truncmode	Define different strategies used by various truncation and compression algorithms for hmatrices and h2matrices
C_uniform	Representation of an admissible block for $\mathcal H^2$ -matrices
C_vert_list	Simple singly connected list to efficiently store a list of vertices