strncat Wformat-overflow warning when using gcc 8.2.1
I'm using gcc 8.2.1 and trying to build this code:
std::string dir = "Documents";
char * _tempname = static_cast <char*> (malloc( dir.length() + 14));
strncpy (_tempname, dir.c_str(), dir.length()+1 );
strncat (_tempname, "/hellooXXXXXX", 13);
but it gives me this warning:
warning:
'char* strncat(char*, const char*, size_t)'specified bound
13 equals source length [-Wstringop-overflow=]
After searching I found that it's an overflow problem to have the size_t equals the source length according to the discussion in this link but I couldn't understand why this is considered a problem and why this overflows the destination. And how could I remove this warning without changing my code?
c++ string gcc gcc-warning gcc8
edited Nov 21 '18 at 9:24
Rai
9441722
asked Nov 21 '18 at 9:07
Amr EssamAmr Essam
83
add a comment |
I'm using gcc 8.2.1 and trying to build this code:
std::string dir = "Documents";
char * _tempname = static_cast <char*> (malloc( dir.length() + 14));
strncpy (_tempname, dir.c_str(), dir.length()+1 );
strncat (_tempname, "/hellooXXXXXX", 13);
but it gives me this warning:
warning:
'char* strncat(char*, const char*, size_t)'specified bound
13 equals source length [-Wstringop-overflow=]
After searching I found that it's an overflow problem to have the size_t equals the source length according to the discussion in this link but I couldn't understand why this is considered a problem and why this overflows the destination. And how could I remove this warning without changing my code?
c++ string gcc gcc-warning gcc8
edited Nov 21 '18 at 9:24
Rai
9441722
asked Nov 21 '18 at 9:07
Amr EssamAmr Essam
83
2
strncatexpects a C-string as a first argument, but you're passing some uninitialized char array to it. Also why you're allocating memory manually when you could simply dostd::string tempname = dir + "/hellooXXXXXX"?
– HolyBlackCat
Nov 21 '18 at 9:12
I forgot a line of code and I edited it now sorry, regarding the code why I'm not using string, actually I'm maintaining this code not writing it from scratch.
– Amr Essam
Nov 21 '18 at 9:16
add a comment |
I'm using gcc 8.2.1 and trying to build this code:
std::string dir = "Documents";
char * _tempname = static_cast <char*> (malloc( dir.length() + 14));
strncpy (_tempname, dir.c_str(), dir.length()+1 );
strncat (_tempname, "/hellooXXXXXX", 13);
but it gives me this warning:
warning:
'char* strncat(char*, const char*, size_t)'specified bound
13 equals source length [-Wstringop-overflow=]
After searching I found that it's an overflow problem to have the size_t equals the source length according to the discussion in this link but I couldn't understand why this is considered a problem and why this overflows the destination. And how could I remove this warning without changing my code?
c++ string gcc gcc-warning gcc8
edited Nov 21 '18 at 9:24
Rai
9441722
asked Nov 21 '18 at 9:07
Amr EssamAmr Essam
83
I'm using gcc 8.2.1 and trying to build this code:
std::string dir = "Documents";
char * _tempname = static_cast <char*> (malloc( dir.length() + 14));
strncpy (_tempname, dir.c_str(), dir.length()+1 );
strncat (_tempname, "/hellooXXXXXX", 13);
but it gives me this warning:
warning:
'char* strncat(char*, const char*, size_t)'specified bound
13 equals source length [-Wstringop-overflow=]
After searching I found that it's an overflow problem to have the size_t equals the source length according to the discussion in this link but I couldn't understand why this is considered a problem and why this overflows the destination. And how could I remove this warning without changing my code?
c++ string gcc gcc-warning gcc8
c++ string gcc gcc-warning gcc8
edited Nov 21 '18 at 9:24
Rai
9441722
asked Nov 21 '18 at 9:07
Amr EssamAmr Essam
83
edited Nov 21 '18 at 9:24
Rai
9441722
asked Nov 21 '18 at 9:07
Amr EssamAmr Essam
83
edited Nov 21 '18 at 9:24
Rai
9441722
edited Nov 21 '18 at 9:24
Rai
9441722
edited Nov 21 '18 at 9:24
Rai
9441722
9441722
asked Nov 21 '18 at 9:07
Amr EssamAmr Essam
83
asked Nov 21 '18 at 9:07
Amr EssamAmr Essam
83
asked Nov 21 '18 at 9:07
Amr EssamAmr Essam
83
83
2
strncatexpects a C-string as a first argument, but you're passing some uninitialized char array to it. Also why you're allocating memory manually when you could simply dostd::string tempname = dir + "/hellooXXXXXX"?
– HolyBlackCat
Nov 21 '18 at 9:12
I forgot a line of code and I edited it now sorry, regarding the code why I'm not using string, actually I'm maintaining this code not writing it from scratch.
– Amr Essam
Nov 21 '18 at 9:16
add a comment |
2
strncatexpects a C-string as a first argument, but you're passing some uninitialized char array to it. Also why you're allocating memory manually when you could simply dostd::string tempname = dir + "/hellooXXXXXX"?
– HolyBlackCat
Nov 21 '18 at 9:12
I forgot a line of code and I edited it now sorry, regarding the code why I'm not using string, actually I'm maintaining this code not writing it from scratch.
– Amr Essam
Nov 21 '18 at 9:16
2
2
strncat expects a C-string as a first argument, but you're passing some uninitialized char array to it. Also why you're allocating memory manually when you could simply do std::string tempname = dir + "/hellooXXXXXX"?– HolyBlackCat
Nov 21 '18 at 9:12
strncat expects a C-string as a first argument, but you're passing some uninitialized char array to it. Also why you're allocating memory manually when you could simply do std::string tempname = dir + "/hellooXXXXXX"?– HolyBlackCat
Nov 21 '18 at 9:12
I forgot a line of code and I edited it now sorry, regarding the code why I'm not using string, actually I'm maintaining this code not writing it from scratch.
– Amr Essam
Nov 21 '18 at 9:16
I forgot a line of code and I edited it now sorry, regarding the code why I'm not using string, actually I'm maintaining this code not writing it from scratch.
– Amr Essam
Nov 21 '18 at 9:16
add a comment |
3 Answers
3
active
oldest
votes
Apparently GCC understands that strncat(_tempname, "/hellooXXXXXX", 13); is no different from strcat(_tempname, "/hellooXXXXXX");, and finds it suspicious that you're using former instead of the latter.
If you can change the code, use strcat instead (or even better, rewrite the thing to use std::string).
If you can't change the code, use -Wno-stringop-overflow flag to disable the warning.
answered Nov 21 '18 at 9:34
HolyBlackCatHolyBlackCat
16.7k33468
add a comment |
The function expects the space left in the destination not the length of the source string, so use
// ...
strncat(_tempname, "/hellooXXXXXX", dir.length() + 14 - strlen(_tempname) - 1);`
instead. No, forget that. Use std::string instead.
answered Nov 21 '18 at 9:25
SwordfishSwordfish
1
add a comment |
my understanding is that gcc issues this warning only because it's a common mistake for users to set the bound equal to the src length, nothing more.
answered Nov 21 '18 at 9:36
Yomna KahwaYomna Kahwa
1
add a comment |
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3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
Apparently GCC understands that strncat(_tempname, "/hellooXXXXXX", 13); is no different from strcat(_tempname, "/hellooXXXXXX");, and finds it suspicious that you're using former instead of the latter.
If you can change the code, use strcat instead (or even better, rewrite the thing to use std::string).
If you can't change the code, use -Wno-stringop-overflow flag to disable the warning.
answered Nov 21 '18 at 9:34
HolyBlackCatHolyBlackCat
16.7k33468
add a comment |
Apparently GCC understands that strncat(_tempname, "/hellooXXXXXX", 13); is no different from strcat(_tempname, "/hellooXXXXXX");, and finds it suspicious that you're using former instead of the latter.
If you can change the code, use strcat instead (or even better, rewrite the thing to use std::string).
If you can't change the code, use -Wno-stringop-overflow flag to disable the warning.
answered Nov 21 '18 at 9:34
HolyBlackCatHolyBlackCat
16.7k33468
add a comment |
Apparently GCC understands that strncat(_tempname, "/hellooXXXXXX", 13); is no different from strcat(_tempname, "/hellooXXXXXX");, and finds it suspicious that you're using former instead of the latter.
If you can change the code, use strcat instead (or even better, rewrite the thing to use std::string).
If you can't change the code, use -Wno-stringop-overflow flag to disable the warning.
answered Nov 21 '18 at 9:34
HolyBlackCatHolyBlackCat
16.7k33468
Apparently GCC understands that strncat(_tempname, "/hellooXXXXXX", 13); is no different from strcat(_tempname, "/hellooXXXXXX");, and finds it suspicious that you're using former instead of the latter.
If you can change the code, use strcat instead (or even better, rewrite the thing to use std::string).
If you can't change the code, use -Wno-stringop-overflow flag to disable the warning.
answered Nov 21 '18 at 9:34
HolyBlackCatHolyBlackCat
16.7k33468
answered Nov 21 '18 at 9:34
HolyBlackCatHolyBlackCat
16.7k33468
answered Nov 21 '18 at 9:34
HolyBlackCatHolyBlackCat
16.7k33468
answered Nov 21 '18 at 9:34
HolyBlackCatHolyBlackCat
16.7k33468
16.7k33468
add a comment |
add a comment |
The function expects the space left in the destination not the length of the source string, so use
// ...
strncat(_tempname, "/hellooXXXXXX", dir.length() + 14 - strlen(_tempname) - 1);`
instead. No, forget that. Use std::string instead.
answered Nov 21 '18 at 9:25
SwordfishSwordfish
1
add a comment |
The function expects the space left in the destination not the length of the source string, so use
// ...
strncat(_tempname, "/hellooXXXXXX", dir.length() + 14 - strlen(_tempname) - 1);`
instead. No, forget that. Use std::string instead.
answered Nov 21 '18 at 9:25
SwordfishSwordfish
1
add a comment |
The function expects the space left in the destination not the length of the source string, so use
// ...
strncat(_tempname, "/hellooXXXXXX", dir.length() + 14 - strlen(_tempname) - 1);`
instead. No, forget that. Use std::string instead.
answered Nov 21 '18 at 9:25
SwordfishSwordfish
1
The function expects the space left in the destination not the length of the source string, so use
// ...
strncat(_tempname, "/hellooXXXXXX", dir.length() + 14 - strlen(_tempname) - 1);`
instead. No, forget that. Use std::string instead.
answered Nov 21 '18 at 9:25
SwordfishSwordfish
1
edited Nov 21 '18 at 9:30
answered Nov 21 '18 at 9:25
SwordfishSwordfish
1
answered Nov 21 '18 at 9:25
SwordfishSwordfish
1
answered Nov 21 '18 at 9:25
SwordfishSwordfish
1
1
add a comment |
add a comment |
my understanding is that gcc issues this warning only because it's a common mistake for users to set the bound equal to the src length, nothing more.
answered Nov 21 '18 at 9:36
Yomna KahwaYomna Kahwa
1
add a comment |
my understanding is that gcc issues this warning only because it's a common mistake for users to set the bound equal to the src length, nothing more.
answered Nov 21 '18 at 9:36
Yomna KahwaYomna Kahwa
1
add a comment |
my understanding is that gcc issues this warning only because it's a common mistake for users to set the bound equal to the src length, nothing more.
answered Nov 21 '18 at 9:36
Yomna KahwaYomna Kahwa
1
my understanding is that gcc issues this warning only because it's a common mistake for users to set the bound equal to the src length, nothing more.
answered Nov 21 '18 at 9:36
Yomna KahwaYomna Kahwa
1
answered Nov 21 '18 at 9:36
Yomna KahwaYomna Kahwa
1
answered Nov 21 '18 at 9:36
Yomna KahwaYomna Kahwa
1
answered Nov 21 '18 at 9:36
Yomna KahwaYomna Kahwa
1
1
add a comment |
add a comment |
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2
strncatexpects a C-string as a first argument, but you're passing some uninitialized char array to it. Also why you're allocating memory manually when you could simply dostd::string tempname = dir + "/hellooXXXXXX"?– HolyBlackCat
Nov 21 '18 at 9:12
I forgot a line of code and I edited it now sorry, regarding the code why I'm not using string, actually I'm maintaining this code not writing it from scratch.
– Amr Essam
Nov 21 '18 at 9:16