Convert part of a string to int in one command in C
I have a long string where I know the location of start and end of an integer. I want to extract the integer and store it in a variable. This is how I can do it now.
//MY_STRING, INT_START, INT_END are the string, start
//position of the int and end position respectively.
char * temp;
strncpy(temp, MY_STRING+INT_START, INT_END-INT_START);
int n = atoi(temp);
The question is can I do this in one line, instead of using a temp string?
c string parsing
asked Nov 23 '18 at 7:58
user38161user38161
82
add a comment |
I have a long string where I know the location of start and end of an integer. I want to extract the integer and store it in a variable. This is how I can do it now.
//MY_STRING, INT_START, INT_END are the string, start
//position of the int and end position respectively.
char * temp;
strncpy(temp, MY_STRING+INT_START, INT_END-INT_START);
int n = atoi(temp);
The question is can I do this in one line, instead of using a temp string?
c string parsing
asked Nov 23 '18 at 7:58
user38161user38161
82
3
Why "one line"..specifically?
– Sourav Ghosh
Nov 23 '18 at 8:02
Maybe atoi can automatically detect the end of a number: atoi(MY_STRING+INT_START). In online GDB it works.
– A.R.C.
Nov 23 '18 at 8:03
1
Be aware thatstrncpyis not a safer version ofstrcpy. You may end up with a non NUL terminated string. Read carefully the strncpy documentation
– Jabberwocky
Nov 23 '18 at 8:13
2
If you really need a one liner that does error checking, you can simply write your own parsing functions, and even differentiate different types and formats (parse_u32,parse_float,parse_hex16). Then you'll have a one liner which does what it's supposed to do.
– Groo
Nov 23 '18 at 8:14
add a comment |
I have a long string where I know the location of start and end of an integer. I want to extract the integer and store it in a variable. This is how I can do it now.
//MY_STRING, INT_START, INT_END are the string, start
//position of the int and end position respectively.
char * temp;
strncpy(temp, MY_STRING+INT_START, INT_END-INT_START);
int n = atoi(temp);
The question is can I do this in one line, instead of using a temp string?
c string parsing
asked Nov 23 '18 at 7:58
user38161user38161
82
I have a long string where I know the location of start and end of an integer. I want to extract the integer and store it in a variable. This is how I can do it now.
//MY_STRING, INT_START, INT_END are the string, start
//position of the int and end position respectively.
char * temp;
strncpy(temp, MY_STRING+INT_START, INT_END-INT_START);
int n = atoi(temp);
The question is can I do this in one line, instead of using a temp string?
c string parsing
c string parsing
asked Nov 23 '18 at 7:58
user38161user38161
82
asked Nov 23 '18 at 7:58
user38161user38161
82
asked Nov 23 '18 at 7:58
user38161user38161
82
asked Nov 23 '18 at 7:58
user38161user38161
82
asked Nov 23 '18 at 7:58
user38161user38161
82
82
3
Why "one line"..specifically?
– Sourav Ghosh
Nov 23 '18 at 8:02
Maybe atoi can automatically detect the end of a number: atoi(MY_STRING+INT_START). In online GDB it works.
– A.R.C.
Nov 23 '18 at 8:03
1
Be aware thatstrncpyis not a safer version ofstrcpy. You may end up with a non NUL terminated string. Read carefully the strncpy documentation
– Jabberwocky
Nov 23 '18 at 8:13
2
If you really need a one liner that does error checking, you can simply write your own parsing functions, and even differentiate different types and formats (parse_u32,parse_float,parse_hex16). Then you'll have a one liner which does what it's supposed to do.
– Groo
Nov 23 '18 at 8:14
add a comment |
3
Why "one line"..specifically?
– Sourav Ghosh
Nov 23 '18 at 8:02
Maybe atoi can automatically detect the end of a number: atoi(MY_STRING+INT_START). In online GDB it works.
– A.R.C.
Nov 23 '18 at 8:03
1
Be aware thatstrncpyis not a safer version ofstrcpy. You may end up with a non NUL terminated string. Read carefully the strncpy documentation
– Jabberwocky
Nov 23 '18 at 8:13
2
If you really need a one liner that does error checking, you can simply write your own parsing functions, and even differentiate different types and formats (parse_u32,parse_float,parse_hex16). Then you'll have a one liner which does what it's supposed to do.
– Groo
Nov 23 '18 at 8:14
3
3
Why "one line"..specifically?
– Sourav Ghosh
Nov 23 '18 at 8:02
Why "one line"..specifically?
– Sourav Ghosh
Nov 23 '18 at 8:02
Maybe atoi can automatically detect the end of a number: atoi(MY_STRING+INT_START). In online GDB it works.
– A.R.C.
Nov 23 '18 at 8:03
Maybe atoi can automatically detect the end of a number: atoi(MY_STRING+INT_START). In online GDB it works.
– A.R.C.
Nov 23 '18 at 8:03
1
1
Be aware that
strncpy is not a safer version of strcpy. You may end up with a non NUL terminated string. Read carefully the strncpy documentation– Jabberwocky
Nov 23 '18 at 8:13
Be aware that
strncpy is not a safer version of strcpy. You may end up with a non NUL terminated string. Read carefully the strncpy documentation– Jabberwocky
Nov 23 '18 at 8:13
2
2
If you really need a one liner that does error checking, you can simply write your own parsing functions, and even differentiate different types and formats (
parse_u32, parse_float, parse_hex16). Then you'll have a one liner which does what it's supposed to do.– Groo
Nov 23 '18 at 8:14
If you really need a one liner that does error checking, you can simply write your own parsing functions, and even differentiate different types and formats (
parse_u32, parse_float, parse_hex16). Then you'll have a one liner which does what it's supposed to do.– Groo
Nov 23 '18 at 8:14
add a comment |
2 Answers
2
active
oldest
votes
can I do this in one line, instead of using a temp string?
Use sscanf() for a quick dirty no-temp.
int n;
// v--- scan width limit
// | v---------------v
if (sscanf(MY_STRING + INT_START, "%*d", INT_END-INT_START, &n) == 1) {
puts("Success");
}
Better code would consider trouble with overflow.
OP's code is no good as temp is not certain to point to a string. It may lack a null character.
strncpy(temp, MY_STRING+INT_START, INT_END-INT_START);
int n = atoi(temp); // bad
answered Nov 23 '18 at 8:03
chuxchux
82.8k872149
1
Well, but this is 4 lines scnr
– moooeeeep
Nov 23 '18 at 8:04
1
@moooeeeep but I guess the requirement was to avoid the temp string...so this should be okay.
– Sourav Ghosh
Nov 23 '18 at 8:05
@moooeeeep At least the conversion happens in one line/command.
– chux
Nov 23 '18 at 8:10
INT_END and INT_START are supposed to check for null character. They come from a token generator.
– user38161
Nov 23 '18 at 8:26
add a comment |
No, you cannot do it in one line and the number of source code lines is most often an irrelevant metric. The only things that matter are safety, readability and performance. strncpy and atoi are both unsafe functions.
The correct way to do this is however quite similar:
int strn_to_int (const char* src, size_t n)
{
char str [LARGE_ENOUGH];
memcpy(str, src, n);
str[n] = '';
return strtol(str, NULL, 10);
}
...
int n = strn_to_int (&MY_STRING[INT_START], INT_END-INT_START);
answered Nov 23 '18 at 8:41
LundinLundin
109k17160265
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
can I do this in one line, instead of using a temp string?
Use sscanf() for a quick dirty no-temp.
int n;
// v--- scan width limit
// | v---------------v
if (sscanf(MY_STRING + INT_START, "%*d", INT_END-INT_START, &n) == 1) {
puts("Success");
}
Better code would consider trouble with overflow.
OP's code is no good as temp is not certain to point to a string. It may lack a null character.
strncpy(temp, MY_STRING+INT_START, INT_END-INT_START);
int n = atoi(temp); // bad
answered Nov 23 '18 at 8:03
chuxchux
82.8k872149
1
Well, but this is 4 lines scnr
– moooeeeep
Nov 23 '18 at 8:04
1
@moooeeeep but I guess the requirement was to avoid the temp string...so this should be okay.
– Sourav Ghosh
Nov 23 '18 at 8:05
@moooeeeep At least the conversion happens in one line/command.
– chux
Nov 23 '18 at 8:10
INT_END and INT_START are supposed to check for null character. They come from a token generator.
– user38161
Nov 23 '18 at 8:26
add a comment |
can I do this in one line, instead of using a temp string?
Use sscanf() for a quick dirty no-temp.
int n;
// v--- scan width limit
// | v---------------v
if (sscanf(MY_STRING + INT_START, "%*d", INT_END-INT_START, &n) == 1) {
puts("Success");
}
Better code would consider trouble with overflow.
OP's code is no good as temp is not certain to point to a string. It may lack a null character.
strncpy(temp, MY_STRING+INT_START, INT_END-INT_START);
int n = atoi(temp); // bad
answered Nov 23 '18 at 8:03
chuxchux
82.8k872149
1
Well, but this is 4 lines scnr
– moooeeeep
Nov 23 '18 at 8:04
1
@moooeeeep but I guess the requirement was to avoid the temp string...so this should be okay.
– Sourav Ghosh
Nov 23 '18 at 8:05
@moooeeeep At least the conversion happens in one line/command.
– chux
Nov 23 '18 at 8:10
INT_END and INT_START are supposed to check for null character. They come from a token generator.
– user38161
Nov 23 '18 at 8:26
add a comment |
can I do this in one line, instead of using a temp string?
Use sscanf() for a quick dirty no-temp.
int n;
// v--- scan width limit
// | v---------------v
if (sscanf(MY_STRING + INT_START, "%*d", INT_END-INT_START, &n) == 1) {
puts("Success");
}
Better code would consider trouble with overflow.
OP's code is no good as temp is not certain to point to a string. It may lack a null character.
strncpy(temp, MY_STRING+INT_START, INT_END-INT_START);
int n = atoi(temp); // bad
answered Nov 23 '18 at 8:03
chuxchux
82.8k872149
can I do this in one line, instead of using a temp string?
Use sscanf() for a quick dirty no-temp.
int n;
// v--- scan width limit
// | v---------------v
if (sscanf(MY_STRING + INT_START, "%*d", INT_END-INT_START, &n) == 1) {
puts("Success");
}
Better code would consider trouble with overflow.
OP's code is no good as temp is not certain to point to a string. It may lack a null character.
strncpy(temp, MY_STRING+INT_START, INT_END-INT_START);
int n = atoi(temp); // bad
answered Nov 23 '18 at 8:03
chuxchux
82.8k872149
edited Nov 23 '18 at 8:07
answered Nov 23 '18 at 8:03
chuxchux
82.8k872149
answered Nov 23 '18 at 8:03
chuxchux
82.8k872149
answered Nov 23 '18 at 8:03
chuxchux
82.8k872149
82.8k872149
1
Well, but this is 4 lines scnr
– moooeeeep
Nov 23 '18 at 8:04
1
@moooeeeep but I guess the requirement was to avoid the temp string...so this should be okay.
– Sourav Ghosh
Nov 23 '18 at 8:05
@moooeeeep At least the conversion happens in one line/command.
– chux
Nov 23 '18 at 8:10
INT_END and INT_START are supposed to check for null character. They come from a token generator.
– user38161
Nov 23 '18 at 8:26
add a comment |
1
Well, but this is 4 lines scnr
– moooeeeep
Nov 23 '18 at 8:04
1
@moooeeeep but I guess the requirement was to avoid the temp string...so this should be okay.
– Sourav Ghosh
Nov 23 '18 at 8:05
@moooeeeep At least the conversion happens in one line/command.
– chux
Nov 23 '18 at 8:10
INT_END and INT_START are supposed to check for null character. They come from a token generator.
– user38161
Nov 23 '18 at 8:26
1
1
Well, but this is 4 lines scnr
– moooeeeep
Nov 23 '18 at 8:04
Well, but this is 4 lines scnr
– moooeeeep
Nov 23 '18 at 8:04
1
1
@moooeeeep but I guess the requirement was to avoid the temp string...so this should be okay.
– Sourav Ghosh
Nov 23 '18 at 8:05
@moooeeeep but I guess the requirement was to avoid the temp string...so this should be okay.
– Sourav Ghosh
Nov 23 '18 at 8:05
@moooeeeep At least the conversion happens in one line/command.
– chux
Nov 23 '18 at 8:10
@moooeeeep At least the conversion happens in one line/command.
– chux
Nov 23 '18 at 8:10
INT_END and INT_START are supposed to check for null character. They come from a token generator.
– user38161
Nov 23 '18 at 8:26
INT_END and INT_START are supposed to check for null character. They come from a token generator.
– user38161
Nov 23 '18 at 8:26
add a comment |
No, you cannot do it in one line and the number of source code lines is most often an irrelevant metric. The only things that matter are safety, readability and performance. strncpy and atoi are both unsafe functions.
The correct way to do this is however quite similar:
int strn_to_int (const char* src, size_t n)
{
char str [LARGE_ENOUGH];
memcpy(str, src, n);
str[n] = '';
return strtol(str, NULL, 10);
}
...
int n = strn_to_int (&MY_STRING[INT_START], INT_END-INT_START);
answered Nov 23 '18 at 8:41
LundinLundin
109k17160265
add a comment |
No, you cannot do it in one line and the number of source code lines is most often an irrelevant metric. The only things that matter are safety, readability and performance. strncpy and atoi are both unsafe functions.
The correct way to do this is however quite similar:
int strn_to_int (const char* src, size_t n)
{
char str [LARGE_ENOUGH];
memcpy(str, src, n);
str[n] = '';
return strtol(str, NULL, 10);
}
...
int n = strn_to_int (&MY_STRING[INT_START], INT_END-INT_START);
answered Nov 23 '18 at 8:41
LundinLundin
109k17160265
add a comment |
No, you cannot do it in one line and the number of source code lines is most often an irrelevant metric. The only things that matter are safety, readability and performance. strncpy and atoi are both unsafe functions.
The correct way to do this is however quite similar:
int strn_to_int (const char* src, size_t n)
{
char str [LARGE_ENOUGH];
memcpy(str, src, n);
str[n] = '';
return strtol(str, NULL, 10);
}
...
int n = strn_to_int (&MY_STRING[INT_START], INT_END-INT_START);
answered Nov 23 '18 at 8:41
LundinLundin
109k17160265
No, you cannot do it in one line and the number of source code lines is most often an irrelevant metric. The only things that matter are safety, readability and performance. strncpy and atoi are both unsafe functions.
The correct way to do this is however quite similar:
int strn_to_int (const char* src, size_t n)
{
char str [LARGE_ENOUGH];
memcpy(str, src, n);
str[n] = '';
return strtol(str, NULL, 10);
}
...
int n = strn_to_int (&MY_STRING[INT_START], INT_END-INT_START);
answered Nov 23 '18 at 8:41
LundinLundin
109k17160265
edited Nov 23 '18 at 10:06
answered Nov 23 '18 at 8:41
LundinLundin
109k17160265
answered Nov 23 '18 at 8:41
LundinLundin
109k17160265
answered Nov 23 '18 at 8:41
LundinLundin
109k17160265
109k17160265
add a comment |
add a comment |
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3
Why "one line"..specifically?
– Sourav Ghosh
Nov 23 '18 at 8:02
Maybe atoi can automatically detect the end of a number: atoi(MY_STRING+INT_START). In online GDB it works.
– A.R.C.
Nov 23 '18 at 8:03
1
Be aware that
strncpyis not a safer version ofstrcpy. You may end up with a non NUL terminated string. Read carefully the strncpy documentation– Jabberwocky
Nov 23 '18 at 8:13
2
If you really need a one liner that does error checking, you can simply write your own parsing functions, and even differentiate different types and formats (
parse_u32,parse_float,parse_hex16). Then you'll have a one liner which does what it's supposed to do.– Groo
Nov 23 '18 at 8:14