Error handling¶

+

PROJ maintains an internal error state, which is local to a +PJ_CONTEXT thread context.

+

See Quick start for more information about how to create and use a thread +context object.

+

If you receive an abnormal return from a PROJ API function (e.g. a NULL +pointer) you may wish to discover more information about the error.

+

In this case you can make a call to proj_context_errno(), passing in +your thread context. This will return an integer error code.

+

If the error code is zero, the last PROJ operation was deemed successful and no +error has been detected.

+

If the error code is non-zero, an error has been detected. You can pass your +thread context together with this error code to +proj_context_errno_string() to retrieve a string describing the error +condition.

+

A basic example showing how a C program might catch and report errors follows:

+

errorhandling.c¶

+

  #include <stdio.h>
+  #include <proj.h>
+
+  int main (void) {
+      PJ_CONTEXT *c;
+      PJ *p;
+      int errno;
+      const char *errstr;
+
+      c = proj_context_create();
+      p = proj_create_crs_to_crs(c, "EPSG:4326", "EPSG:3857", NULL);
+
+      if (p == 0) {
+          /* Something is wrong, let's try to get details ... */
+          errno = proj_context_errno(c);
+          if (errno == 0) {
+              /* This should be impossible. */
+              fprintf(stderr, "Failed to create transformation, reason unknown.\n");
+          } else {
+              errstr = proj_context_errno_string(c, errno);
+              fprintf(stderr, "Failed to create transformation: %s.\n", errstr);
+          }
+          proj_context_destroy(c);
+          return 1;
+      }
+
+      /* transformation object is valid, do work ... */
+
+      proj_destroy(p);
+      proj_context_destroy(c);
+
+      return 0;
+  }
+

+

+

+ + +

+