An Issue about char* or char**

[Mr-JingShi]

scrcpy/app/src/server.c

Line 193 in b4caa48

char *p = (char *) &cmd[count]; \

I am confused about &cmd[count]，then I test

https://www.onlinegdb.com/

include <iostream>
#include <typeinfo>

int main()
{
    const char *cmd[128] = {0};
    
    std::cout << typeid(&cmd[0]).name() << std::endl;
    std::cout << std::is_same<decltype(&cmd[0]), const char**>::value << std::endl;
    
    {
        std::cout << "--test 1--" << std::endl;
        char *p = (char *) &cmd[0];
        if (asprintf(&p, "bit_rate=%d", 100) == -1) {
            std::cout << "error" << std::endl;
        }
        std:: cout << "p:" << (p ? p : "null") << std::endl;
        std:: cout << "cmd[0]:" << (cmd[0] ? cmd[0] : "null") << std::endl;
        free(p);
    }
    
    {
        std::cout << "--test 2--" << std::endl;
        char *p = 0;
        if (asprintf(&p, "bit_rate=%d", 100) == -1) {
            std::cout << "error" << std::endl;
        }
        std:: cout << "p:" << (p ? p : "null") << std::endl;
        std:: cout << "cmd[0]:" << (cmd[0] ? cmd[0] : "null") << std::endl;
        free(p);
    }
    
    {
        std::cout << "--test 3--" << std::endl;
        char *p = (char *) cmd[0];
        if (asprintf(&p, "bit_rate=%d", 100) == -1) {
            std::cout << "error" << std::endl;
        }
        std:: cout << "p:" << (p ? p : "null") << std::endl;
        std:: cout << "cmd[0]:" << (cmd[0] ? cmd[0] : "null") << std::endl;
        free(p);
    }
    
    {
        std::cout << "--test 4--" << std::endl;
        char **p = (char **) &cmd[0];
        if (asprintf(p, "bit_rate=%d", 100) == -1) {
            std::cout << "error" << std::endl;
        }
        std:: cout << "*p:" << (*p ? *p : "null") << std::endl;
        std:: cout << "cmd[0]:" << (cmd[0] ? cmd[0] : "null") << std::endl;
        free(*p);
    }

    return 0;
}

PKc
1
--test 1--
p:bit_rate=100
cmd[0]:null
--test 2--
p:bit_rate=100
cmd[0]:null
--test 3--
p:bit_rate=100
cmd[0]:null
--test 4--
*p:bit_rate=100
cmd[0]:bit_rate=100

We can use test 2、4 case, why test 1 case?

[rom1v]

Indeed, this code is flawed. It is a mix of:

diff --git a/app/src/server.c b/app/src/server.c
index 76e83c6f9..9d4fb098a 100644
--- a/app/src/server.c
+++ b/app/src/server.c
@@ -213,9 +213,9 @@ execute_server(struct sc_server *server,
     cmd[count++] = SCRCPY_VERSION;
 
     unsigned dyn_idx = count; // from there, the strings are allocated
 #define ADD_PARAM(fmt, ...) { \
-        char *p = (char *) &cmd[count]; \
+        char *p; \
         if (asprintf(&p, fmt, ## __VA_ARGS__) == -1) { \
             goto end; \
         } \
         cmd[count++] = p; \

diff --git a/app/src/server.c b/app/src/server.c
index 76e83c6f9..9e5b39ae3 100644
--- a/app/src/server.c
+++ b/app/src/server.c
@@ -214,11 +214,11 @@ execute_server(struct sc_server *server,
 
     unsigned dyn_idx = count; // from there, the strings are allocated
 #define ADD_PARAM(fmt, ...) { \
-        char *p = (char *) &cmd[count]; \
-        if (asprintf(&p, fmt, ## __VA_ARGS__) == -1) { \
+        char **p = (char **) &cmd[count]; \
+        if (asprintf(p, fmt, ## __VA_ARGS__) == -1) { \
             goto end; \
         } \
-        cmd[count++] = p; \
+        count++; \
     }
 
     ADD_PARAM("scid=%08x", params->scid);

It did not cause problems, because even if p was initialized with a garbage value, it was never read.

Thank you for your report.

Fixed by b5d41ad.