IDebugExpressionContext2::ParseText

Article
01/12/2024

Parses an expression in text form for later evaluation.

Syntax

int ParseText(
    string                pszCode,
    enum_PARSEFLAGS       dwFlags,
    uint                  nRadix,
    out IDebugExpression2 ppExpr,
    out string            pbstrError,
    out uint              pichError
);

HRESULT ParseText(
    LPCOLESTR           pszCode,
    PARSEFLAGS          dwFlags,
    UINT                nRadix,
    IDebugExpression2** ppExpr,
    BSTR*               pbstrError,
    UINT*               pichError
);

Parameters

pszCode
[in] The expression to be parsed.

dwFlags
[in] A combination of flags from the PARSEFLAGS enumeration that controls parsing.

nRadix
[in] The radix to be used in parsing any numerical information in pszCode.

ppExpr
[out] Returns the IDebugExpression2 object that represents the parsed expression, which is ready for binding and evaluation.

pbstrError
[out] Returns the error message if the expression contains an error.

pichError
[out] Returns the character index of the error in pszCode if the expression contains an error.

Return Value

If successful, returns S_OK; otherwise, returns an error code.

Remarks

When this method is called, a debug engine (DE) should parse the expression and validate it for correctness. The pbstrError and pichError parameters may be filled in if the expression is invalid.

Note that the expression is not evaluated, only parsed. A later call to the EvaluateSync or EvaluateAsync methods evaluates the parsed expression.

Example

The following example shows how to implement this method for a simple CEnvBlock object that exposes the IDebugExpressionContext2 interface. This example considers the expression to be parsed as the name of an environment variable and retrieves the value from that variable.

HRESULT CEnvBlock::ParseText(
    LPCOLESTR           pszCode,
    PARSEFLAGS          dwFlags,
    UINT                nRadix,
    IDebugExpression2 **ppExpr,
    BSTR               *pbstrError,
    UINT               *pichError)
{
    HRESULT hr = E_OUTOFMEMORY;
    // Create an integer variable with a value equal to one plus
    // twice the length of the passed expression to be parsed.
    int iAnsiLen      = 2 * (wcslen(pszCode)) + 1;
    // Allocate a character string of the same length.
    char *pszAnsiCode = (char *) malloc(iAnsiLen);

    // Check for successful memory allocation.
    if (pszAnsiCode) {
        // Map the wide-character pszCode string to the new pszAnsiCode character string.
        WideCharToMultiByte(CP_ACP, 0, pszCode, -1, pszAnsiCode, iAnsiLen, NULL, NULL);
        // Check to see if the app can successfully get the environment variable.
        if (GetEnv(pszAnsiCode)) {

            // Create and initialize a CExpression object.
            CComObject<CExpression> *pExpr;
            CComObject<CExpression>::CreateInstance(&pExpr);
            pExpr->Init(pszAnsiCode, this, NULL);

            // Assign the pointer to the new object to the passed argument
            // and AddRef the object.
            *ppExpr = pExpr;
            (*ppExpr)->AddRef();
            hr = S_OK;
        // If the program cannot successfully get the environment variable.
        } else {
            // Set the errror message and return E_FAIL.
            *pbstrError = SysAllocString(L"No such environment variable.");
            hr = E_FAIL;
        }
        // Free the local character string.
        free(pszAnsiCode);
    }
    return hr;
}

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