C语言常见内存错误及解决方法-飞外网

本文将带您了解一些良好的和内存相关的编码实践，以将内存错误保持在控制范围内。内存错误是 C 和 C++ 编程的祸根：它们很普遍，认识其严重性已有二十多年，但始终没有彻底解决，它们可能严重影响应用程序，并且很少有开发团队对其制定明确的管理计划。但好消息是，它们并不怎么神秘。

引言

C 和 C++ 程序中的内存错误非常有害：它们很常见，并且可能导致严重的后果。来自计算机应急响应小组(请参见参考资料)和供应商的许多最严重的安全公告都是由简单的内存错误造成的。自从 70 年代末期以来，C 程序员就一直讨论此类错误，但其影响在至今年仍然很大。更糟的是，如果按我的思路考虑，当今的许多 C 和 C++ 程序员可能都会认为内存错误是不可控制而又神秘的顽症，它们只能纠正，无法预防。

/* Allocate once, free twice. */void f3(){ char *p; p = malloc(10); ... free(p); ... free(p); } /* Allocate zero times, free once. */void f4(){ char *p; /* Note that p remains uninitialized here. */ free(p);}

这些错误通常也不太严重。尽管 C 标准在这些情形中没有定义具体行为，但典型的实现将忽略错误，或者快速而明确地对它们进行标记;总之，这些都是安全情形。悬空指针

/********* ...** Note that any function invoking protected_file_read()* assumes responsibility eventually to fclose() its* return value, UNLESS that value is NULL.*********/FILE *protected_file_read(char *filename){ FILE *fp; fp = fopen(filename, "r"); if (fp) {... } else {... } return fp;} /******** ...** Note that the return value of get_message points to a* fixed memory location. Do NOT free() it; remember to* make a copy if it must be retained ...*********/char *get_message(){ static char this_buffer[400]; ... (void) sprintf(this_buffer, ...); return this_buffer; } /********* ...* While this function uses heap memory, and so * temporarily might expand the over-all memory* footprint, it properly cleans up after itself.* ********/ int f6(char *item1){ my_class c1; int result; ... c1 = new my_class(item1); ... result = c1.x; delete c1; return result;}/********* ...* Note that f8() is documented to return a value* which needs to be returned to heap; as f7 thinly* wraps f8, any code which invokes f7() must be* careful to free() the return value.*********/int *f7(){ int *p; p = f8(...); ... return p;}

static char *important_pointer = NULL;void f9(){ if (!important_pointer) important_pointer = malloc(IMPORTANT_SIZE); ... if (condition) /* Ooops! We just lost the reference important_pointer already held. */important_pointer = malloc(DIFFERENT_SIZE); ...}