A label names a position in code so control can refer to it or transfer to it. In C, labels and goto statements work together inside the same function. section 17.3
A label can repeat a block
RETRY: marks the position where execution resumes when goto RETRY is taken. The marked position is also relevant to object lifetime: an object defined in the surrounding block remains alive across the repeated execution, unlike an object defined inside a while statement. section 17.3
Labels have parallel roles at two language levels:
- C labels identify destinations for goto within one function. section 17.3
- Assembler labels identify points such as a function entry or a translated C goto destination; .L_AGAIN corresponds to the C label AGAIN. section 13.5
1 size_t* ip = 0
2 while(something)
3 ip = &(size_t){ fun() }; /* Life ends with while */
4 /* Good: resource is freed */
5 printf("i is %d", *ip) /* Bad: object is dead */
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Compare a loop-defined object with a goto-repeated block to see how the label changes execution structure and affects object lifetime. section 17.3
