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annotate mupdf-source/docs/reference/c/fitz/error.md @ 22:d77477b4e151

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Let _int_rc() also handle (i.e. ignore) a local version suffix
author Franz Glasner <fzglas.hg@dom66.de>
date Fri, 19 Sep 2025 12:05:57 +0200
parents b50eed0cc0ef
children
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1 # Errors
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3 MuPDF uses a `setjmp` based exception handling system. This is encapsulated by
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4 the use of three macros: `fz_try`, `fz_always`, and `fz_catch`. When an error
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5 is raised by `fz_throw`, or re-raised by `fz_rethrow`, execution will jump to
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6 the enclosing always/catch block.
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8 All functions you call should be guarded by a `fz_try` block to catch the
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9 errors, or the program will call `exit()` on errors. You don't want that.
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11 The `fz_always` block is optional. It is typically used to free memory or
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12 release resources unconditionally, in both the case when the execution of the
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13 try block succeeds, and when an error occurs.
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15 fz_try(ctx) {
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16 // Do stuff that may throw an exception.
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17 }
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18 fz_always(ctx) {
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19 // This (optional) block is always executed.
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20 }
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21 fz_catch(ctx) {
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22 // This block is only executed when recovering from an exception.
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23 }
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26 Since the `fz_try` macro is based on `setjmp`, the same conditions that apply
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27 to local variables in the presence of `setjmp` apply. Any locals written to
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28 inside the try block may be restored to their pre-try state when an error
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29 occurs. We provide a `fz_var()` macro to guard against this.
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31 In the following example, if we don't guard `buf` with `fz_var`, then when an
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32 error occurs the `buf` local variable might have be reset to its pre-try value
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33 (`NULL`) and we would leak the memory.
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35 char *buf = NULL;
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37 fz_var(buf);
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39 fz_try(ctx) {
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40 buf = fz_malloc(ctx, 100);
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41 // Do stuff with buf that may throw an exception.
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42 }
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43 fz_always(ctx) {
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44 fz_free(ctx, buf);
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45 }
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46 fz_catch(ctx) {
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47 fz_rethrow(ctx);
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48 }
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50 Carefully note that you should **never** return from within a `fz_try` or
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51 `fz_always block`! Doing so will unbalance the exception stack, and things will
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52 go catastrophically wrong. Instead, it is possible to break out of the `fz_try`
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53 and `fz_always` block by using a break statement if you want to exit the block
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54 early without throwing an exception.
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56 Throwing a new exception can be done with `fz_throw`. Passing an exception
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57 along after having cleaned up in the `fz_catch` block can be done with
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58 `fz_rethrow`. `fz_throw` takes a `printf`-like formatting string.
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60 enum {
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61 FZ_ERROR_SYSTEM, // fatal out of memory or syscall error
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62 FZ_ERROR_LIBRARY, // unclassified error from third-party library
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63 FZ_ERROR_ARGUMENT, // invalid or out-of-range arguments to functions
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64 FZ_ERROR_LIMIT, // failed because of resource or other hard limits
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65 FZ_ERROR_UNSUPPORTED, // tried to use an unsupported feature
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66 FZ_ERROR_FORMAT, // syntax or format errors that are unrecoverable
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67 FZ_ERROR_SYNTAX, // syntax errors that should be diagnosed and ignored
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68 };
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70 void fz_throw(fz_context *ctx, int error_code, const char *fmt, ...);
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71 void fz_rethrow(fz_context *ctx);