ADG ADG - 2 months ago 9
C++ Question

Segmentation Fault when variables are not-null but on `callq`

Update on Question:
Here is the SSCCE where I receive

SIGSEV
on
str1_h[0][j] = bar1(str1_c[j]);
. All variables are not-null which I checked using gdb:

#include <fstream> //ifstream and ofilestream

using namespace std;

int bar1(int);
int bar2(int);
int bar3(int);

int main() {
string str1 = "string";
ifstream ifs;
ifs.open("./file.txt");
string line, str2;
while (!ifs.eof()) {
ifs >> line;
str2 += line;
}
ifs.close();
unsigned str2_l = str2.length();
unsigned str1_l = str1.length();
unsigned n = str2_l - str1_l + 1;
int str1_c[4];
str1_c[0] = 0;
str1_c[1] = 0;
str1_c[2] = 0;
str1_c[3] = 0;
int x[3][4][n];
int str1_h[3][4];
for (unsigned j = 0; j < 4; j++) {
str1_h[0][j] = bar1(str1_c[j]);
str1_h[1][j] = bar2(str1_c[j]);
str1_h[2][j] = bar3(str1_c[j]);
for (unsigned i = 0; i < n; i++) {
x[0][j][i] = bar1(0);
x[1][j][i] = bar2(0);
x[2][j][i] = bar3(0);
}
}
}
int bar1(int x) {
return 0;
}
int bar2(int x) {
return 0;
}
int bar3(int x) {
return 0;
}

Answer

You cannot have a dynamic array on the stack in C++:

int x[3][4][n];

either use new, or use an STL container (e.g. std::vector). See also How do I declare a 2d array in C++ using new?

Your array x is on the stack, thus writing to this array will likely overwrite important values on the stack (e.g. return pointers etc.)