Page History

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• strncpy() instead of strcpy()
• strncat() instead of strcat()
• fgets() instead of gets()
• snprintf() instead of sprintf()

These function truncate strings that exceed the specified limits. Additionally, some functions such as {{strncpy()}} do not guarantee that the resulting string is null-terminated \[[STR33-C

|STR33-C. Guarantee that all strings are null-terminated]\].
Truncation results in a loss of data, and in some cases, leads to software vulnerabilities.

Non-Compliant Code Example

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char *string_data;
char a[16];
...
strncpy(a, string_data, sizeof(a));

Compliant Solution 1

Truncation resulting from a string copy operation should be treated as an error condition.

#define A_SIZE 16
char *string_data;
char a[A_SIZE];
...
if (string_data) {
  if (strlen(string_data) < A_SIZEsizeof(a)) {
    strcpy(a, string_data);
  }
  else {
    /* handle string too large condition */
  }
}
else {
  /* handle null string condition */
}

Compliant Solution 2

Example using strcpy()

Compliant Solution 3

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Wiki Markup
The {{strcpy_s()}} function provides additional safeguards including accepting the size of the destination buffer as an additional argument \[[STR00-A|STR00-A. Use TR 24731 for remediation of existing string manipulation code]\].

Code Block
#define A_SIZE 16 char *string_data; char a[A_SIZE]; ... if (string_data) { if (strlen(string_data) < sizeof(a)) { strcpy(a, sizeof(a), string_data); } else { /* handle string too large condition */ } } else { /* handle null string condition */ }

Exception

An exception to this rule applies if the intent of the programmer was to intentionally truncate the null-terminated byte string. To be compliant with this standard, this intent must be made clear statement in comments.

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