realloc function problem

Ayman Mashal

Hi i have a function that gets a parameter of type (char **ptr) i want to reallocate the space for this pointer (reduce or increase) i have the followig code that raise an error when realloc change the original pointer **(*ptr)=(char *)realloc(*ptr,(originalLength+shift) * sizeof(char));** what is the problem in this line note : its work fine when realloc returns the same pointer ? thanks

blue_rabbit

I have a idea. Are you sure ptr is not null (0) before you call realloc. Because if ptr is NULL (0) then when you call *ptr is wrong. you can add a code to report that ptr is null like this: if(!ptr) MessageBox(0,"ptr is null","error",0);

prasad_som

Can you show how this memory is previously allocated, and used (code)? Possibly, its getting corrupted due to using it wrong way.

Prasad Notifier using ATL | Operator new[],delete[][^]

Ayman Mashal

no its not null because when i debug the code *ptr contains a string . and kindly note the the realloc code that i added is used in many calls before for the same array and its work fine when the array size is in smaller size but if i added some characters to it then the allocation failed and i get the error (if i added one character !!) i think this happen when realloc moves the array to another place and returns a new pointer ?

blue_rabbit

yeh, so how you add character to this pointer. If possible, you can copy your code and paste here. It is hard to explain if you only talk without code. Ah, I think maybe you allocated memory before for *ptr by another function like *ptr = new char[]. Don't you do that. If it's, it's wrong. -- modified at 3:41 Sunday 4th March, 2007

Ayman Mashal

the array is created by adding characters using the following function void Append(char **buffer,int size,char c) { (*buffer)=(char *)realloc(*buffer,(size+1) * sizeof(char)); (*buffer)[size-1]=c; (*buffer)[size]='\0'; } after the array is created i am running the function that raise the error several times and its work fine and i increase and decrease its content using the following function : void replaceStr(char **replaceIn,char *replaceWith,int fromIndx,int toIndx) { char *ptr=(*replaceIn)+fromIndx; int replaceWithLen=(replaceWith==NULL)?0:strlen(replaceWith); int replacedStrLen=toIndx-fromIndx; int originalStrLen=strlen(*replaceIn); //int str3Len=strlen(str3); int shift=replaceWithLen-replacedStrLen; int bytesToMove=strlen(ptr)+1; int originalLength; printf("%s\n",*replaceIn); if(replaceWithLen==0) { memmove(ptr-1,ptr+replacedStrLen,bytesToMove); } else { if(replaceWithLen>replacedStrLen) { originalLength=strlen(*replaceIn); **(*replaceIn)=(char *)realloc(*replaceIn,(originalLength+shift+1) * sizeof(char));** if(*replaceIn==NULL) printf("Error while allocating memory"); *((*replaceIn)+originalStrLen)='\0'; ptr=(*replaceIn)+fromIndx; memmove(ptr+replaceWithLen,ptr+replacedStrLen,bytesToMove); } else memmove(ptr+replaceWithLen,ptr+replacedStrLen,bytesToMove); } memcpy(ptr,replaceWith,replaceWithLen); } the error happen at some point in the line in bold ! -- modified at 4:21 Sunday 4th March, 2007

Ayman Mashal

the array is created by adding characters using the following function void Append(char **buffer,int size,char c) { (*buffer)=(char *)realloc(*buffer,(size+1) * sizeof(char)); (*buffer)[size-1]=c; (*buffer)[size]='\0'; } after the array is created i am running the function that raise the error several times and its work fine and i increase and decrease its content using the following function : void replaceStr(char **replaceIn,char *replaceWith,int fromIndx,int toIndx) { char *ptr=(*replaceIn)+fromIndx; int replaceWithLen=(replaceWith==NULL)?0:strlen(replaceWith); int replacedStrLen=toIndx-fromIndx; int originalStrLen=strlen(*replaceIn); //int str3Len=strlen(str3); int shift=replaceWithLen-replacedStrLen; int bytesToMove=strlen(ptr)+1; int originalLength; printf("%s\n",*replaceIn); if(replaceWithLen==0) { memmove(ptr-1,ptr+replacedStrLen,bytesToMove); } else { if(replaceWithLen>replacedStrLen) { originalLength=strlen(*replaceIn); (*replaceIn)=(char *)realloc(*replaceIn,(originalLength+shift+1) * sizeof(char)); if(*replaceIn==NULL) printf("Error while allocating memory"); *((*replaceIn)+originalStrLen)='\0'; ptr=(*replaceIn)+fromIndx; memmove(ptr+replaceWithLen,ptr+replacedStrLen,bytesToMove); } else memmove(ptr+replaceWithLen,ptr+replacedStrLen,bytesToMove); } memcpy(ptr,replaceWith,replaceWithLen); } the error happen at some point in the line in bold !

blue_rabbit

you have to give me an example that raises error. I try your code with my example:

int main(){	
	char *lpstr1 = 0,*lpstr2 = 0;
	lpstr1 = (char *)malloc(10);
	lpstr2 = (char *)malloc(20);
	strcpy(lpstr2,"damnit");
	strcpy(lpstr1,"kha");	
	replaceStr(&lpstr1,lpstr2,2,10);
	cout<<"str1 "<

there is no problem. I think your code is hard to read. I do not understand, what do you want when replaceWithLen = 0, i think you dont have to do any think. The logic is complex. I think you need a new version. I write this code, I hope it matchs your will. Please try it. void myreplaceStr(char **replaceIn,char *replaceWith,int fromIndx,int toIndx){ if((replaceWith==0)||(replaceIn==0)){ printf("%s","nothing to do here\n"); return; } // if(*replaceIn == 0){ printf("%s","nothing will modified here\n"); return; } // if(fromIndx > strlen(*replaceIn)){ printf("%s","index outside of string, commonly we dont want this happen\n"); } //if we donot have enough memory in *replaceIn DWORD minSize = (strlen(replaceWith) > toIndx - fromIndx) ? (toIndx-fromIndx+1): strlen(replaceWith); if(strlen(replaceWith+fromIndx) < minSize){ *replaceIn = (char *)realloc(*replaceIn,strlen(*replaceIn + fromIndx) + minSize); } //now we have enough memory in *replace to contain replaceWith we just copy it memcpy(*replaceIn + fromIndx,replaceWith,strlen(replaceWith)); }; -- modified at 6:21 Sunday 4th March, 2007