Before you scoff, consider that some exceptions betray a condition so severe that reasonable recovery is unlikely anyway. Perhaps the best example is malloc of a small object returning NULL. If the free store manager can't scrape together a few spare contiguous bytes, your C庫頭文件＜stdlib.h＞提供了兩個(gè)不是相當(dāng)完美的程序函數(shù)：abort與exit，這些函數(shù)實(shí)現(xiàn)了異常的生命期在第4、5階段。兩者不返回它的調(diào)用者，并且結(jié)束程序。
By having two classes of return values, setjmp lets you determine how it's being used. When setting j, setjmp works as you normally expect; but as the target of a long jump, setjmp "wakes up" from outside its normal context. 假如使用longjmp來引發(fā)終止異常，setjmpgoto到正確的異常處理方法里。
#include ＜setjmp.h＞ #include ＜stdio.h＞
jmp_buf j; void raise_exception（void） { printf（"exception raised/n"）; longjmp（j, 1）; /* jump to exception handler */ printf（"this line should never appear/n"）; }
int main（void） { if （setjmp（j） == 0） { printf（"'setjmp' is initializing 'j'/n"）; raise_exception（）;//Restore context printf（"this line should never appear/n"）; } else { printf（"'setjmp' was just jumped into/n"）; /* this code is the exception handler */ } return 0; }
/* 運(yùn)行結(jié)果:
'setjmp' is initializing 'j' exception raised 'setjmp' was just jumped into */
int main（void） { double x, y, result; /* ... somehow set 'x' and 'y' ... */ errno = 0; result = pow（x, y）; if （errno == EDOM） printf（"domain error on x/y pair/n"）; else if （errno == ERANGE） printf（"range error on result/n"）; else printf（"x to the y = %d/n", （int） result）; return 0; }
說明：errno不需要引用到對象：
int *_errno_function（） { static int real_errno = 0; return &real_errno;//不需要這樣做 }
#define errno （*_errno_function（））
int main（void） { errno = 0; /* ... */ if （errno == EDOM） /* ... */ } 返回值與參數(shù)
