Memory--剖析程序在内存中的存储

1MemoryAllocationCS217MemoryAllocation•Goodprogrammersmakeefficientuseofmemory•UnderstandingmemoryallocationisimportantCreatedatastructuresofarbitrarysizeAvoid“memoryleaks”Run-timeperformance2Memory•Whatismemory?Flip-flopsstoringbitsforvariables,data,code,etc.CPUMemoryDiskNetworkVideoAudioDataBusMemory•Whatismemory?Flip-flopsstoringbitsforvariables,data,code,etc.UnixprovidesvirtualmemoryCPUMemoryDiskNetworkVideoAudioDataBus00xffffffffVirtualAddressSpace3Memory•Whatisstoredinmemory?00xffffffffVirtualAddressSpaceMemory•Whatisstoredinmemory?CodeConstantsGlobalandstaticvariablesLocalvariablesDynamicmemory(malloc)00xffffffffVirtualAddressSpaceintiSize;char*f(void){char*p;iSize=8;p=malloc(iSize);returnp;}globallocalconstantdynamic4MemoryLayout•Howismemoryorganized?CodeConstantsGlobalandstaticvariablesLocalvariablesDynamicmemory(malloc)00xffffffffintiSize;char*f(void){char*p;iSize=8;p=malloc(iSize);returnp;}MemoryLayout•Howismemoryorganized?Text=codeData=constantsBSS=globalandstaticvariablesStack=localvariablesHeap=dynamicmemory00xffffffffTextDataBSSStackHeapintiSize;char*f(void){char*p;iSize=8;p=malloc(iSize);returnp;}bssstackdataheap5MemoryAllocation•Howismemoryallocated?Globalandstaticvariables=programstartupLocalvariables=functioncallDynamicmemory=malloc()00xffffffffTextDataBSSStackHeapMemoryAllocationallocatedinBSS,settozeroatstartupallocatedonstackatstartoffunctionf8bytesallocatedinheapbymallocintiSize;char*f(void){char*p;iSize=8;p=malloc(iSize);returnp;}6MemoryDeallocation•Howismemorydeallocated?Globalandstaticvariables=programfinishLocalvariables=functionreturnDynamicmemory=free()•AllmemoryisdeallocatedatprogramterminationItisgoodstyletofreeallocatedmemoryanywayMemoryDeallocationavailableuntilprogramterminationdeallocatedbyreturnfromfunctionfdeallocatebycallingfree(p)intiSize;char*f(void){char*p;iSize=8;p=malloc(iSize);returnp;}7DynamicMemory#includestdlib.hvoid*malloc(size_tsize);voidfree(void*ptr);Heapchar*str=malloc(8);...free(str);8str8BytesforDataDynamicMemory#includestdlib.hvoid*malloc(size_tsize);voidfree(void*ptr);00xffffffffTextDataBSSStack}HeapHeapchar*p1=malloc(3);char*p2=malloc(1);char*p3=malloc(4);free(p2);char*p4=malloc(6);free(p3);char*p5=malloc(2);free(p1);free(p4);free(p5);8DynamicMemory#includestdlib.hvoid*malloc(size_tsize);voidfree(void*ptr);00xffffffffTextDataBSSStack}HeapHeapchar*p1=malloc(3);char*p2=malloc(1);char*p3=malloc(4);free(p2);char*p4=malloc(6);free(p3);char*p5=malloc(2);free(p1);free(p4);free(p5);p1DynamicMemory#includestdlib.hvoid*malloc(size_tsize);voidfree(void*ptr);00xffffffffTextDataBSSStack}HeapHeapchar*p1=malloc(3);char*p2=malloc(1);char*p3=malloc(4);free(p2);char*p4=malloc(6);free(p3);char*p5=malloc(2);free(p1);free(p4);free(p5);p1p29DynamicMemory#includestdlib.hvoid*malloc(size_tsize);voidfree(void*ptr);00xffffffffTextDataBSSStack}HeapHeapchar*p1=malloc(3);char*p2=malloc(1);char*p3=malloc(4);free(p2);char*p4=malloc(6);free(p3);char*p5=malloc(2);free(p1);free(p4);free(p5);p1p2p3DynamicMemory#includestdlib.hvoid*malloc(size_tsize);voidfree(void*ptr);00xffffffffTextDataBSSStack}HeapHeapchar*p1=malloc(3);char*p2=malloc(1);char*p3=malloc(4);free(p2);char*p4=malloc(6);free(p3);char*p5=malloc(2);free(p1);free(p4);free(p5);p1p2p310DynamicMemory#includestdlib.hvoid*malloc(size_tsize);voidfree(void*ptr);00xffffffffTextDataBSSStack}HeapHeapchar*p1=malloc(3);char*p2=malloc(1);char*p3=malloc(4);free(p2);char*p4=malloc(6);free(p3);char*p5=malloc(2);free(p1);free(p4);free(p5);p1p2p3p4DynamicMemory#includestdlib.hvoid*malloc(size_tsize);voidfree(void*ptr);00xffffffffTextDataBSSStack}HeapHeapchar*p1=malloc(3);char*p2=malloc(1);char*p3=malloc(4);free(p2);char*p4=malloc(6);free(p3);char*p5=malloc(2);free(p1);free(p4);free(p5);p1p2p3p411DynamicMemory#includestdlib.hvoid*malloc(size_tsize);voidfree(void*ptr);00xffffffffTextDataBSSStack}HeapHeapchar*p1=malloc(3);char*p2=malloc(1);char*p3=malloc(4);free(p2);char*p4=malloc(6);free(p3);char*p5=malloc(2);free(p1);free(p4);free(p5);p1p5,p2p3p4DynamicMemory#includestdlib.hvoid*malloc(size_tsize);voidfree(void*ptr);00xffffffffTextDataBSSStack}HeapHeapchar*p1=malloc(3);char*p2=malloc(1);char*p3=malloc(4);free(p2);char*p4=malloc(6);free(p3);char*p5=malloc(2);free(p1);free(p4);free(p5);p1p5,p2p3p412DynamicMemory#includestdlib.hvoid*malloc(size_tsize);voidfree(void*ptr);00xffffffffTextDataBSSStack}HeapHeapchar*p1=malloc(3);char*p2=malloc(1);char*p3=malloc(4);free(p2);char*p4=malloc(6);free(p3);char*p5=malloc(2);free(p1);free(p4);free(p5);p1p5,p2p3p4DynamicMemory#includestdlib.hvoid*malloc(size_tsize);voidfree(void*ptr);00xffffffffTextDataBSSStack}HeapHeapchar*p1=malloc(3);char*p2=malloc(1);char*p3=malloc(4);free(p2);char*p4=malloc(6);free(p3);char*p5=malloc(2);free(p1);free(p4);free(p5);p1p5,p2p3p413ExampleCodeI00xffffffffTextDataBSSStackHeap...voidReadStrings(Array_Tstrings,FILE*fp){charbuffer[MAX_STRING_LENGTH];while(fgets(buffer,MAX_STRING_LENGTH,fp)){Array_insert(strings,buffer);}}...intmain(