CODEWITHSUNDEEP
c++exec
Danny Milosavljevic
Danny Milosavljevic

Reputation: 642

std::string -> execvp etc

I just found an elusive bug in a program and it turned out to be because with optimization enabled, in something like the following sometimes the std::string is destroyed before processDocument() got the text out of it:

#include <stdio.h>
#include <spawn.h>
#include <string>
static void processDocument(const char* text) {
        const char* const argv[] = {
                "echo",
                text,
                NULL,
        };
        pid_t p;
        posix_spawnp(&p, "echo", NULL, NULL, (char**) argv, environ);
}
static int mark = 'A';
static void createDocument() {
        const char* vc;
        std::string v = "ABCKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKK42";
        ++mark;
        v[0] = mark;
        vc = v.c_str();
        processDocument(vc);
}
int main() {
        createDocument();
        createDocument();
        return(0);
}

How do I safely convert a std::string to a char* for use in execvp, posix_spawnp etc ?

Upvotes: 0

Views: 405

Answers (1)

Danny Milosavljevic
Danny Milosavljevic

Reputation: 642

I found out why it really was (here the actual minimal testcase):

std::string resultString;
const char* nodeText;
const char* altText;
resultString = "......whatever1.";
nodeText = resultString.c_str();
resultString = ".....whatever2..";
altText = resultString.c_str();
printf("%s\n", nodeText); // garbage

Bad idea.

Upvotes: 1

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