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| <h4 class="subsection">12.12.10 Parsing a Template String</h4> |
| |
| <p><a name="index-parsing-a-template-string-1046"></a> |
| You can use the function <code>parse_printf_format</code> to obtain |
| information about the number and types of arguments that are expected by |
| a given template string. This function permits interpreters that |
| provide interfaces to <code>printf</code> to avoid passing along invalid |
| arguments from the user's program, which could cause a crash. |
| |
| <p>All the symbols described in this section are declared in the header |
| file <samp><span class="file">printf.h</span></samp>. |
| |
| <!-- printf.h --> |
| <!-- GNU --> |
| <div class="defun"> |
| — Function: size_t <b>parse_printf_format</b> (<var>const char *template, size_t n, int *argtypes</var>)<var><a name="index-parse_005fprintf_005fformat-1047"></a></var><br> |
| <blockquote><p>This function returns information about the number and types of |
| arguments expected by the <code>printf</code> template string <var>template</var>. |
| The information is stored in the array <var>argtypes</var>; each element of |
| this array describes one argument. This information is encoded using |
| the various ‘<samp><span class="samp">PA_</span></samp>’ macros, listed below. |
| |
| <p>The argument <var>n</var> specifies the number of elements in the array |
| <var>argtypes</var>. This is the maximum number of elements that |
| <code>parse_printf_format</code> will try to write. |
| |
| <p><code>parse_printf_format</code> returns the total number of arguments required |
| by <var>template</var>. If this number is greater than <var>n</var>, then the |
| information returned describes only the first <var>n</var> arguments. If you |
| want information about additional arguments, allocate a bigger |
| array and call <code>parse_printf_format</code> again. |
| </p></blockquote></div> |
| |
| <p>The argument types are encoded as a combination of a basic type and |
| modifier flag bits. |
| |
| <!-- printf.h --> |
| <!-- GNU --> |
| <div class="defun"> |
| — Macro: int <b>PA_FLAG_MASK</b><var><a name="index-PA_005fFLAG_005fMASK-1048"></a></var><br> |
| <blockquote><p>This macro is a bitmask for the type modifier flag bits. You can write |
| the expression <code>(argtypes[i] & PA_FLAG_MASK)</code> to extract just the |
| flag bits for an argument, or <code>(argtypes[i] & ~PA_FLAG_MASK)</code> to |
| extract just the basic type code. |
| </p></blockquote></div> |
| |
| <p>Here are symbolic constants that represent the basic types; they stand |
| for integer values. |
| |
| <dl> |
| <!-- printf.h --> |
| <!-- GNU --> |
| <dt><code>PA_INT</code><a name="index-PA_005fINT-1049"></a><dd>This specifies that the base type is <code>int</code>. |
| |
| <!-- printf.h --> |
| <!-- GNU --> |
| <br><dt><code>PA_CHAR</code><a name="index-PA_005fCHAR-1050"></a><dd>This specifies that the base type is <code>int</code>, cast to <code>char</code>. |
| |
| <!-- printf.h --> |
| <!-- GNU --> |
| <br><dt><code>PA_STRING</code><a name="index-PA_005fSTRING-1051"></a><dd>This specifies that the base type is <code>char *</code>, a null-terminated string. |
| |
| <!-- printf.h --> |
| <!-- GNU --> |
| <br><dt><code>PA_POINTER</code><a name="index-PA_005fPOINTER-1052"></a><dd>This specifies that the base type is <code>void *</code>, an arbitrary pointer. |
| |
| <!-- printf.h --> |
| <!-- GNU --> |
| <br><dt><code>PA_FLOAT</code><a name="index-PA_005fFLOAT-1053"></a><dd>This specifies that the base type is <code>float</code>. |
| |
| <!-- printf.h --> |
| <!-- GNU --> |
| <br><dt><code>PA_DOUBLE</code><a name="index-PA_005fDOUBLE-1054"></a><dd>This specifies that the base type is <code>double</code>. |
| |
| <!-- printf.h --> |
| <!-- GNU --> |
| <br><dt><code>PA_LAST</code><a name="index-PA_005fLAST-1055"></a><dd>You can define additional base types for your own programs as offsets |
| from <code>PA_LAST</code>. For example, if you have data types ‘<samp><span class="samp">foo</span></samp>’ |
| and ‘<samp><span class="samp">bar</span></samp>’ with their own specialized <code>printf</code> conversions, |
| you could define encodings for these types as: |
| |
| <pre class="smallexample"> #define PA_FOO PA_LAST |
| #define PA_BAR (PA_LAST + 1) |
| </pre> |
| </dl> |
| |
| <p>Here are the flag bits that modify a basic type. They are combined with |
| the code for the basic type using inclusive-or. |
| |
| <dl> |
| <!-- printf.h --> |
| <!-- GNU --> |
| <dt><code>PA_FLAG_PTR</code><a name="index-PA_005fFLAG_005fPTR-1056"></a><dd>If this bit is set, it indicates that the encoded type is a pointer to |
| the base type, rather than an immediate value. |
| For example, ‘<samp><span class="samp">PA_INT|PA_FLAG_PTR</span></samp>’ represents the type ‘<samp><span class="samp">int *</span></samp>’. |
| |
| <!-- printf.h --> |
| <!-- GNU --> |
| <br><dt><code>PA_FLAG_SHORT</code><a name="index-PA_005fFLAG_005fSHORT-1057"></a><dd>If this bit is set, it indicates that the base type is modified with |
| <code>short</code>. (This corresponds to the ‘<samp><span class="samp">h</span></samp>’ type modifier.) |
| |
| <!-- printf.h --> |
| <!-- GNU --> |
| <br><dt><code>PA_FLAG_LONG</code><a name="index-PA_005fFLAG_005fLONG-1058"></a><dd>If this bit is set, it indicates that the base type is modified with |
| <code>long</code>. (This corresponds to the ‘<samp><span class="samp">l</span></samp>’ type modifier.) |
| |
| <!-- printf.h --> |
| <!-- GNU --> |
| <br><dt><code>PA_FLAG_LONG_LONG</code><a name="index-PA_005fFLAG_005fLONG_005fLONG-1059"></a><dd>If this bit is set, it indicates that the base type is modified with |
| <code>long long</code>. (This corresponds to the ‘<samp><span class="samp">L</span></samp>’ type modifier.) |
| |
| <!-- printf.h --> |
| <!-- GNU --> |
| <br><dt><code>PA_FLAG_LONG_DOUBLE</code><a name="index-PA_005fFLAG_005fLONG_005fDOUBLE-1060"></a><dd>This is a synonym for <code>PA_FLAG_LONG_LONG</code>, used by convention with |
| a base type of <code>PA_DOUBLE</code> to indicate a type of <code>long double</code>. |
| </dl> |
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