Access violation reading location NULL in Circuit Satisfiability Solver - c++

Question

I try to resolve the circuit satisfiability problem reading the circuit from file (in the form presented in text visualizer-somehow dynamic). If my circuit is small my resolver work smooth (small means like <16-18 wires). If i get to 25-30 wires so 2^25-30 possibilities i encountered a problem with a violation of access. I tried to free memory every time i can. I tried to create a new pointer of my expression every time, but the access violation always occur.
^ How is this possible ?
int evalBoolExprForBinaryVector(char *expr, int n, int binaryVector[]){
// create boolean expression from logical expression
char* expression = (char*) malloc(sizeof(char) * strlen(expr) + 1);
strcpy(expression, expr);
for(int binaryVectorCounter=0; binaryVectorCounter<n; binaryVectorCounter++){
char* currentSearchedIdentifier = (char*) malloc(sizeof(char) * 10);
char* index =(char*) malloc(sizeof(char) * 10);
char* valueOfIndex = (char*) malloc(sizeof(char)*2);
strcpy(currentSearchedIdentifier,"v[");
sprintf(index, "%d", binaryVectorCounter);
strcat(currentSearchedIdentifier, index);
strcat(currentSearchedIdentifier, "]");
sprintf(valueOfIndex, "%d", binaryVector[binaryVectorCounter]);
expression = str_replace(expression,currentSearchedIdentifier,valueOfIndex);
free(currentSearchedIdentifier);
free(index);
free(valueOfIndex);
}
// here my expression will be something like
// ( 0 | 1 ) & (!0 | !1) & ...
// evaluate this
return evalBoolExpr(expression);
};
Here is my code for better understanding.
The program breaks with this exception in strlen.asm at:
main_loop:
mov eax,dword ptr [ecx] ; read 4 bytes
Thanks in advance for any thoughts.

Answer 1

I rewrite this part in c++ manner and everything worked smooth (some delay but at least it can finish with success)
void replaceAll(std::string& str, const std::string& from, const std::string& to) {
if(from.empty())
return;
size_t start_pos = 0;
while((start_pos = str.find(from, start_pos)) != std::string::npos) {
str.replace(start_pos, from.length(), to);
start_pos += to.length();
}
}
int evalBoolExprForBinaryVector(char *expr, int n, int binaryVector[]){
std::string expression(expr);
for(int binaryVectorCounter=0; binaryVectorCounter<n; binaryVectorCounter++){
std::string currentSearchedIdentifier, valueOfIndex;
currentSearchedIdentifier = "v[" + std::to_string(binaryVectorCounter) + "]";
valueOfIndex = std::to_string(binaryVector[binaryVectorCounter]);
replaceAll(expression,currentSearchedIdentifier,valueOfIndex);
}
char *cstr = new char[expression.length() + 1];
strcpy(cstr, expression.c_str());
return evalBoolExpr(cstr);
};