What causes "[" cimg_appname "_math_parser] CImg ::%s: %s%s %s%s has invalid type '%s' (should be %s), in expression '%s'." in Yalantis/uCrop?

Match the expected type shown in the message: wrap scalars or use [ ] for vectors as needed.

Yalantis/uCrop · error · CImgArgumentException

[" cimg_appname "_math_parser] CImg<%s>::%s: %s%s %s%s has i

Error message

[" cimg_appname "_math_parser] CImg<%s>::%s: %s%s %s%s has invalid type '%s' (should be %s), in expression '%s'.

What it means

The math parser type-checks arguments/operands against the expected kind (scalar or a vector of expected dimension N). When an operand has the wrong type — e.g. a vector where a scalar is required, or a vector of the wrong dimension — this CImgArgumentException is thrown. The message shows the actual type via s_type(arg) and the expected type string.

Source

Thrown at ucrop/src/main/jni/CImg.h:25253

        bool cond = false;
        if (mode&1) cond|=_is_scalar;
        if (mode&2) cond|=_is_vector;
        if (!cond) {
          const char *s_arg;
          if (*s_op!='F') s_arg = !n_arg?"":n_arg==1?"Left-hand":"Right-hand";
          else s_arg = s_argth(n_arg);
          CImg<charT> sb_type(32);
          if (mode==1) cimg_snprintf(sb_type,sb_type._width,"'scalar'");
          else if (mode==2) {
            if (N) cimg_snprintf(sb_type,sb_type._width,"'vector%u'",N);
            else cimg_snprintf(sb_type,sb_type._width,"'vector'");
          } else {
            if (N) cimg_snprintf(sb_type,sb_type._width,"'scalar' or 'vector%u'",N);
            else cimg_snprintf(sb_type,sb_type._width,"'scalar' or 'vector'");
          }
          char *s0;
          _cimg_mp_strerr;
          throw CImgArgumentException("[" cimg_appname "_math_parser] "
                                      "CImg<%s>::%s: %s%s %s%s has invalid type '%s' (should be %s), "
                                      "in expression '%s'.",
                                      pixel_type(),_cimg_mp_calling_function,s_op,*s_op?":":"",
                                      s_arg,*s_op=='F'?(*s_arg?" argument":" Argument"):(*s_arg?" operand":" Operand"),
                                      s_type(arg)._data,sb_type._data,s0);
        }
      }

      // Check that imglist are not empty.
      void check_list(char *const ss, char *const se, const char saved_char) {
        if (!imglist) {
          char *s0;
          _cimg_mp_strerr;
          throw CImgArgumentException("[" cimg_appname "_math_parser] "
                                      "CImg<%s>::%s: %s%s Image list cannot be empty, for expression '%s'.",
                                      pixel_type(),_cimg_mp_calling_function,s_op,*s_op?":":"",s0);
        }
      }

View on GitHub (pinned to f788b534b4)

Solutions

Match the expected type shown in the message: wrap scalars or use [ ] for vectors as needed.
Check the CImg documentation for the exact argument types of the function used.
Correct vector dimension to the required vectorN size.
Test the sub-expression standalone to isolate which operand has the wrong type.

Example fix

// before
img.fill("norm([1,2,3],[4,5])"); // second operand wrong dimension
// after
img.fill("norm([1,2,3],[4,5,6])");

Defensive patterns

Strategy: type-guard

Validate before calling

// Verify operand kind before composing expression
bool scalarOk = std::isfinite(value);

Type guard

bool isScalarArg(const std::string& tok) { return tok.find(',') == std::string::npos && tok.front() != '['; }

Try / catch

try { img.fill(expr); } catch (const cimg_library::CImgArgumentException& e) { /* fix operand type per message */ }

Prevention

Consult function signature docs for scalar vs vector args
Avoid accidental [x] wrapping of scalars
Test sub-expressions in isolation

When it happens

Trigger: Calling an MP function like 'norm(v)' with a matrix-typed value, or passing a vectorN where scalar/vectorM is required, e.g. 'pand(a,[1,2])' with scalar a expected.

Common situations: Typos in expression variables; misremembering function signatures (vector vs scalar args); wrapping constants in brackets producing unintended vectors.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

AI-assisted analysis of Yalantis/uCrop@f788b534b4 (2026-09-08). Data as JSON: /api/errors/7500eb86f41d6ce9. Report an issue: GitHub.