Fix const correctness

As reported by #137

documentation/Mat_GetFileAccessMode.3

@@ -23,7 +23,7 @@
 .\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 .\" OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd October 18, 2023
+.Dd November 20, 2023
 .Dt MAT_GETFILEACCESSMODE 3
 .Os
 .Sh NAME
@@ -33,7 +33,7 @@
 .Fd #include <matio.h>
 .Ft enum mat_acc
 .Fo Mat_GetFileAccessMode
-.Fa "mat_t *matfp"
+.Fa "const mat_t *matfp"
 .Fc
 .Sh DESCRIPTION
 The

documentation/Mat_GetFilename.3

@@ -23,7 +23,7 @@
 .\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 .\" OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd September 12, 2019
+.Dd November 20, 2023
 .Dt MAT_GETFILENAME 3
 .Os
 .Sh NAME
@@ -33,7 +33,7 @@
 .Fd #include <matio.h>
 .Ft const char *
 .Fo Mat_GetFilename
-.Fa "mat_t *matfp"
+.Fa "const mat_t *matfp"
 .Fc	
 .Sh DESCRIPTION
 The

documentation/Mat_GetHeader.3

@@ -23,7 +23,7 @@
 .\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 .\" OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd March 25, 2019
+.Dd November 20, 2023
 .Dt MAT_GETHEADER 3
 .Os
 .Sh NAME
@@ -33,7 +33,7 @@
 .Fd #include <matio.h>
 .Ft const char *
 .Fo Mat_GetHeader
-.Fa "mat_t *matfp"
+.Fa "const mat_t *matfp"
 .Fc
 .Sh DESCRIPTION
 The

documentation/Mat_GetVersion.3

@@ -23,7 +23,7 @@
 .\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 .\" OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd September 12, 2019
+.Dd November 20, 2023
 .Dt MAT_GETVERSION 3
 .Os
 .Sh NAME
@@ -33,7 +33,7 @@
 .Fd #include <matio.h>
 .Ft enum mat_ft
 .Fo Mat_GetVersion
-.Fa "mat_t *matfp"
+.Fa "const mat_t *matfp"
 .Fc
 .Sh DESCRIPTION
 The

documentation/Mat_VarCreate.3

@@ -23,7 +23,7 @@
 .\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 .\" OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd September 12, 2019
+.Dd November 20, 2023
 .Dt MAT_VARCREATE 3
 .Os
 .Sh NAME
@@ -37,8 +37,8 @@
 .Fa "enum matio_classes class_type"
 .Fa "enum matio_types data_type"
 .Fa "int rank"
-.Fa "size_t *dims"
-.Fa "void *data"
+.Fa "const size_t *dims"
+.Fa "const void *data"
 .Fa "int opt"
 .Fc
 .Sh DESCRIPTION

documentation/Mat_VarCreateStruct.3

@@ -23,7 +23,7 @@
 .\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 .\" OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd September 12, 2019
+.Dd November 20, 2023
 .Dt MAT_VARCREATESTRUCT 3
 .Os
 .Sh NAME
@@ -35,7 +35,7 @@
 .Fo Mat_VarCreateStruct
 .Fa "const char *name"
 .Fa "int rank"
-.Fa "size_t *dims"
+.Fa "const size_t *dims"
 .Fa "const char **fields"
 .Fa "unsigned nfields"
 .Fc

documentation/Mat_VarGetNumberOfFields.3

@@ -23,7 +23,7 @@
 .\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 .\" OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd March 18, 2012
+.Dd November 20, 2023
 .Dt MAT_VARGETNUMBEROFFIELDS 3
 .Os
 .Sh NAME
@@ -33,7 +33,7 @@
 .Fd #include <matio.h>
 .Ft unsigned
 .Fo Mat_VarGetNumberOfFields
-.Fa "matvar_t *matvar"
+.Fa "const matvar_t *matvar"
 .Fc
 .Sh DESCRIPTION
 The

documentation/Mat_VarGetSize.3

@@ -23,7 +23,7 @@
 .\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 .\" OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd October 20, 2017
+.Dd November 20, 2023
 .Dt MAT_VARGETSIZE 3
 .Os
 .Sh NAME
@@ -33,7 +33,7 @@
 .Fd #include <matio.h>
 .Ft size_t
 .Fo Mat_VarGetSize
-.Fa "matvar_t *matvar"
+.Fa "const matvar_t *matvar"
 .Fc
 .Sh DESCRIPTION
 The

documentation/Mat_VarGetStructs.3

@@ -23,7 +23,7 @@
 .\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 .\" OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd March 16, 2012
+.Dd November 20, 2023
 .Dt MAT_VARGETSTRUCTS 3
 .Os
 .Sh NAME
@@ -34,9 +34,9 @@
 .Ft matvar_t *
 .Fo Mat_VarGetStructs
 .Fa "const matvar_t *matvar"
-.Fa "int *start"
-.Fa "int *stride"
-.Fa "int *edge"
+.Fa "cons int *start"
+.Fa "const int *stride"
+.Fa "const int *edge"
 .Fa "int copy_fields"
 .Fc
 .Sh DESCRIPTION

documentation/Mat_VarPrint.3

@@ -23,7 +23,7 @@
 .\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 .\" OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd October 20, 2017
+.Dd November 20, 2023
 .Dt MAT_VARPRINT 3
 .Os
 .Sh NAME
@@ -33,7 +33,7 @@
 .Fd #include <matio.h>
 .Ft void
 .Fo Mat_VarPrint
-.Fa "matvar_t *matvar"
+.Fa "const matvar_t *matvar"
 .Fa "int printdata"
 .Fc
 .Sh DESCRIPTION

src/io.c

@@ -45,7 +45,7 @@
 #define va_copy(d, s) memcpy(&(d), &(s), sizeof(va_list))
 #endif
 
-static void (*logfunc)(int log_level, char *message) = NULL;
+static void (*logfunc)(int log_level, const char *message) = NULL;
 static const char *progname = NULL;
 static char *strdup_vprintf(const char *format, va_list ap) MATIO_FORMATATTR_VPRINTF;
 
@@ -122,7 +122,7 @@ utf82u(const char *src)
  * @param message logging message
  */
 static void
-mat_logfunc(int log_level, char *message)
+mat_logfunc(int log_level, const char *message)
 {
     if ( progname ) {
         if ( log_level & MATIO_LOG_LEVEL_CRITICAL ) {
@@ -463,7 +463,7 @@ Mat_LogInit(const char *prog_name)
  * @return 0 on success
  */
 int
-Mat_LogInitFunc(const char *prog_name, void (*log_func)(int log_level, char *message))
+Mat_LogInitFunc(const char *prog_name, void (*log_func)(int log_level, const char *message))
 {
     logfunc = log_func;
     progname = prog_name;