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How should I verify that an integer value passed in from argv won't overflow?

6

0

I have a program that requires the user to enter an integer as a command line argument, in the form of ./program 100.

Obviously this will read the value in as a string, so I need to parse it to an integer. I have to ensure that the input value won't overflow an integer variable. I have read about strtol(), but it works with long variables and I have to stick with a regular int.

Is there anything similar that can be used for an int?

c

share|improve this question

asked 4 hours ago

JakeJake

109212

• 
  
  
  

  
  7
  

  
  
  
  
  
  

  
  
  Use strtol and compare to INT_MAX/MIN.
  
  – Eugene Sh.
  4 hours ago
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  if (longvalue > INT_MAX) /* overflow */; don't forget to #include <limits.h>
  
  – pmg
  4 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @pmg check would fail for platforms when sizeof(int) == sizeof(long) = true.
  
  – SergeyA
  4 hours ago
  
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @pmg, you can do it in a single check by just comparing for >= INT_MAX. This will always work.
  
  – SergeyA
  4 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @SergeyA Yeah, apparently one should handle strtol errors too. I assumed OP is already aware of that when mentioned using strtol.
  
  – Eugene Sh.
  4 hours ago
  

  
  
  
  

 | 
show 10 more comments

6

0

I have a program that requires the user to enter an integer as a command line argument, in the form of ./program 100.

Obviously this will read the value in as a string, so I need to parse it to an integer. I have to ensure that the input value won't overflow an integer variable. I have read about strtol(), but it works with long variables and I have to stick with a regular int.

Is there anything similar that can be used for an int?

c

share|improve this question

asked 4 hours ago

JakeJake

109212

• 
  
  
  

  
  7
  

  
  
  
  
  
  

  
  
  Use strtol and compare to INT_MAX/MIN.
  
  – Eugene Sh.
  4 hours ago
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  if (longvalue > INT_MAX) /* overflow */; don't forget to #include <limits.h>
  
  – pmg
  4 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @pmg check would fail for platforms when sizeof(int) == sizeof(long) = true.
  
  – SergeyA
  4 hours ago
  
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @pmg, you can do it in a single check by just comparing for >= INT_MAX. This will always work.
  
  – SergeyA
  4 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @SergeyA Yeah, apparently one should handle strtol errors too. I assumed OP is already aware of that when mentioned using strtol.
  
  – Eugene Sh.
  4 hours ago
  

  
  
  
  

 | 
show 10 more comments

I have a program that requires the user to enter an integer as a command line argument, in the form of ./program 100.

Obviously this will read the value in as a string, so I need to parse it to an integer. I have to ensure that the input value won't overflow an integer variable. I have read about strtol(), but it works with long variables and I have to stick with a regular int.

Is there anything similar that can be used for an int?

c

share|improve this question

asked 4 hours ago

JakeJake

109212

share|improve this question

asked 4 hours ago

JakeJake

109212

share|improve this question

asked 4 hours ago

JakeJake

109212

asked 4 hours ago

JakeJake

109212

asked 4 hours ago

JakeJake

109212

2 Answers
2

active

oldest

votes

5

You can use strtol for this. You'll first need to check if this function fails to convert the value. If it convert successfully, then check if the value is in the range of INT_MIN to INT_MAX:

errno = 0;

long x = strtol(argv[1], NULL, 10);

if (errno) {

    perror("conversion failed");

} else if (x < INT_MIN) {

    printf("value too smalln");

} else if (x > INT_MAX) {

    printf("value too bign");

} else {

    printf("value = %ldn", x);

}

Note that this will work whether long is the same size as int or larger.

If sizeof(long) > sizeof(int), the INT_MIN and INT_MAX checks will catch the cases where the value fits in a long but not an int. If sizeof(long) == sizeof(int), an out of range value will result in errno being set to non-zero to catch the error, and the INT_MIN and INT_MAX cases will never be true.

share|improve this answer

edited 4 hours ago

Keith Thompson

194k26290484

answered 4 hours ago

dbushdbush

103k13108145

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  Strictly speaking, it's the ranges of int and long that are relevant here, not their sizes. In the presence of padding bits, it's possible for int and long to have the same size, but for long to have a wider range. (Few if any implementations actually use padding bits, though.)
  
  – Keith Thompson
  4 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  if (errno) { is not a sufficient test to detect "conversion failed" as errno can still be 0.
  
  – chux
  1 hour ago
  

  
  
  
  

add a comment | 

1

How should I verify that an integer value passed in from argv won't overflow?

Use strtol() and check the end pointer. Then check errno and maybe a range test

if (argc > 1) {

  char *endptr;

  errno = 0;

  long num = strtol(argv[1], &endptr, 10);



  if (argv[1] == endptr) {

    puts("No conversion");

  } else if (errno == ERANGE) {

    puts("Value outside long range");

  #if LONG_MIN < INT_MIN || LONG_MAX > INT_MAX

  } else if (num < INT_MAX || num > INT_MAX) {

    errno = ERANGE;

    puts("Value outside int range");

  #endif

  } else {

    // If code wants to look for trailing junk

    if (*endptr) {

      puts("Non-numeric text");

    } else {

      printf("Success %dn", (int) num);

    } 

  } 

Based on Why is there no strtoi in stdlib.h?

share|improve this answer

edited 1 hour ago

answered 2 hours ago

chuxchux

84.8k874157

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  #else should be #endif
  
  – chqrlie
  2 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @chqrlie Yes, code amended.
  
  – chux
  1 hour ago
  

  
  
  
  

add a comment | 

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5

You can use strtol for this. You'll first need to check if this function fails to convert the value. If it convert successfully, then check if the value is in the range of INT_MIN to INT_MAX:

errno = 0;

long x = strtol(argv[1], NULL, 10);

if (errno) {

    perror("conversion failed");

} else if (x < INT_MIN) {

    printf("value too smalln");

} else if (x > INT_MAX) {

    printf("value too bign");

} else {

    printf("value = %ldn", x);

}

Note that this will work whether long is the same size as int or larger.

If sizeof(long) > sizeof(int), the INT_MIN and INT_MAX checks will catch the cases where the value fits in a long but not an int. If sizeof(long) == sizeof(int), an out of range value will result in errno being set to non-zero to catch the error, and the INT_MIN and INT_MAX cases will never be true.

share|improve this answer

edited 4 hours ago

Keith Thompson

194k26290484

answered 4 hours ago

dbushdbush

103k13108145

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  Strictly speaking, it's the ranges of int and long that are relevant here, not their sizes. In the presence of padding bits, it's possible for int and long to have the same size, but for long to have a wider range. (Few if any implementations actually use padding bits, though.)
  
  – Keith Thompson
  4 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  if (errno) { is not a sufficient test to detect "conversion failed" as errno can still be 0.
  
  – chux
  1 hour ago
  

  
  
  
  

add a comment | 

5

You can use strtol for this. You'll first need to check if this function fails to convert the value. If it convert successfully, then check if the value is in the range of INT_MIN to INT_MAX:

errno = 0;

long x = strtol(argv[1], NULL, 10);

if (errno) {

    perror("conversion failed");

} else if (x < INT_MIN) {

    printf("value too smalln");

} else if (x > INT_MAX) {

    printf("value too bign");

} else {

    printf("value = %ldn", x);

}

Note that this will work whether long is the same size as int or larger.

If sizeof(long) > sizeof(int), the INT_MIN and INT_MAX checks will catch the cases where the value fits in a long but not an int. If sizeof(long) == sizeof(int), an out of range value will result in errno being set to non-zero to catch the error, and the INT_MIN and INT_MAX cases will never be true.

share|improve this answer

edited 4 hours ago

Keith Thompson

194k26290484

answered 4 hours ago

dbushdbush

103k13108145

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  Strictly speaking, it's the ranges of int and long that are relevant here, not their sizes. In the presence of padding bits, it's possible for int and long to have the same size, but for long to have a wider range. (Few if any implementations actually use padding bits, though.)
  
  – Keith Thompson
  4 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  if (errno) { is not a sufficient test to detect "conversion failed" as errno can still be 0.
  
  – chux
  1 hour ago
  

  
  
  
  

add a comment | 

You can use strtol for this. You'll first need to check if this function fails to convert the value. If it convert successfully, then check if the value is in the range of INT_MIN to INT_MAX:

errno = 0;

long x = strtol(argv[1], NULL, 10);

if (errno) {

    perror("conversion failed");

} else if (x < INT_MIN) {

    printf("value too smalln");

} else if (x > INT_MAX) {

    printf("value too bign");

} else {

    printf("value = %ldn", x);

}

Note that this will work whether long is the same size as int or larger.

If sizeof(long) > sizeof(int), the INT_MIN and INT_MAX checks will catch the cases where the value fits in a long but not an int. If sizeof(long) == sizeof(int), an out of range value will result in errno being set to non-zero to catch the error, and the INT_MIN and INT_MAX cases will never be true.

share|improve this answer

edited 4 hours ago

Keith Thompson

194k26290484

answered 4 hours ago

dbushdbush

103k13108145

errno = 0;

long x = strtol(argv[1], NULL, 10);

if (errno) {

    perror("conversion failed");

} else if (x < INT_MIN) {

    printf("value too smalln");

} else if (x > INT_MAX) {

    printf("value too bign");

} else {

    printf("value = %ldn", x);

}

share|improve this answer

edited 4 hours ago

Keith Thompson

194k26290484

answered 4 hours ago

dbushdbush

103k13108145

edited 4 hours ago

Keith Thompson

194k26290484

edited 4 hours ago

Keith Thompson

194k26290484

answered 4 hours ago

dbushdbush

103k13108145

answered 4 hours ago

dbushdbush

103k13108145

1

How should I verify that an integer value passed in from argv won't overflow?

Use strtol() and check the end pointer. Then check errno and maybe a range test

if (argc > 1) {

  char *endptr;

  errno = 0;

  long num = strtol(argv[1], &endptr, 10);



  if (argv[1] == endptr) {

    puts("No conversion");

  } else if (errno == ERANGE) {

    puts("Value outside long range");

  #if LONG_MIN < INT_MIN || LONG_MAX > INT_MAX

  } else if (num < INT_MAX || num > INT_MAX) {

    errno = ERANGE;

    puts("Value outside int range");

  #endif

  } else {

    // If code wants to look for trailing junk

    if (*endptr) {

      puts("Non-numeric text");

    } else {

      printf("Success %dn", (int) num);

    } 

  } 

Based on Why is there no strtoi in stdlib.h?

share|improve this answer

edited 1 hour ago

answered 2 hours ago

chuxchux

84.8k874157

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  #else should be #endif
  
  – chqrlie
  2 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @chqrlie Yes, code amended.
  
  – chux
  1 hour ago
  

  
  
  
  

add a comment | 

1

How should I verify that an integer value passed in from argv won't overflow?

Use strtol() and check the end pointer. Then check errno and maybe a range test

if (argc > 1) {

  char *endptr;

  errno = 0;

  long num = strtol(argv[1], &endptr, 10);



  if (argv[1] == endptr) {

    puts("No conversion");

  } else if (errno == ERANGE) {

    puts("Value outside long range");

  #if LONG_MIN < INT_MIN || LONG_MAX > INT_MAX

  } else if (num < INT_MAX || num > INT_MAX) {

    errno = ERANGE;

    puts("Value outside int range");

  #endif

  } else {

    // If code wants to look for trailing junk

    if (*endptr) {

      puts("Non-numeric text");

    } else {

      printf("Success %dn", (int) num);

    } 

  } 

Based on Why is there no strtoi in stdlib.h?

share|improve this answer

edited 1 hour ago

answered 2 hours ago

chuxchux

84.8k874157

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  #else should be #endif
  
  – chqrlie
  2 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @chqrlie Yes, code amended.
  
  – chux
  1 hour ago
  

  
  
  
  

add a comment | 

How should I verify that an integer value passed in from argv won't overflow?

Use strtol() and check the end pointer. Then check errno and maybe a range test

if (argc > 1) {

  char *endptr;

  errno = 0;

  long num = strtol(argv[1], &endptr, 10);



  if (argv[1] == endptr) {

    puts("No conversion");

  } else if (errno == ERANGE) {

    puts("Value outside long range");

  #if LONG_MIN < INT_MIN || LONG_MAX > INT_MAX

  } else if (num < INT_MAX || num > INT_MAX) {

    errno = ERANGE;

    puts("Value outside int range");

  #endif

  } else {

    // If code wants to look for trailing junk

    if (*endptr) {

      puts("Non-numeric text");

    } else {

      printf("Success %dn", (int) num);

    } 

  } 

Based on Why is there no strtoi in stdlib.h?

share|improve this answer

edited 1 hour ago

answered 2 hours ago

chuxchux

84.8k874157

if (argc > 1) {

  char *endptr;

  errno = 0;

  long num = strtol(argv[1], &endptr, 10);



  if (argv[1] == endptr) {

    puts("No conversion");

  } else if (errno == ERANGE) {

    puts("Value outside long range");

  #if LONG_MIN < INT_MIN || LONG_MAX > INT_MAX

  } else if (num < INT_MAX || num > INT_MAX) {

    errno = ERANGE;

    puts("Value outside int range");

  #endif

  } else {

    // If code wants to look for trailing junk

    if (*endptr) {

      puts("Non-numeric text");

    } else {

      printf("Success %dn", (int) num);

    } 

  } 

share|improve this answer

edited 1 hour ago

answered 2 hours ago

chuxchux

84.8k874157

answered 2 hours ago

chuxchux

84.8k874157

answered 2 hours ago

chuxchux

84.8k874157